diff --git a/lang/de.yml b/lang/de.yml
index e13317605..e85811b47 100644
--- a/lang/de.yml
+++ b/lang/de.yml
@@ -27,9 +27,22 @@ de:
   SilverStripe\Control\RequestProcessor:
     INVALID_REQUEST: 'Ungültige Anfrage'
     REQUEST_ABORTED: 'Anfrage abgebrochen'
+  SilverStripe\Dev\DevBuildController:
+    CAN_DEV_BUILD_DESCRIPTION: 'Darf /dev/build ausführen'
+    CAN_DEV_BUILD_HELP: 'Darf den Build-Befehl ausführen (/dev/build).'
+  SilverStripe\Dev\DevConfigController:
+    CAN_DEV_CONFIG_DESCRIPTION: 'Darf /dev/config anzeigen'
+    CAN_DEV_CONFIG_HELP: 'Darf die gesamte Anwendungskonfiguration einsehen (/dev/config).'
   SilverStripe\Dev\DevConfirmationController:
     INFO_DESCRIPTION: 'Bestätige potenziell gefährliche Aktion'
     INFO_TITLE: Sicherheitsbestätigung
+  SilverStripe\Dev\DevelopmentAdmin:
+    ALL_DEV_ADMIN_DESCRIPTION: 'Darf alle /dev-Endpunkte anzeigen und ausführen'
+    ALL_DEV_ADMIN_HELP: 'Darf alle /dev-Endpunkte anzeigen und ausführen'
+    PERMISSIONS_CATEGORY: 'Dev Berechtigungen'
+  SilverStripe\Dev\TaskRunner:
+    BUILDTASK_CAN_RUN_DESCRIPTION: 'Darf alle /dev/tasks anzeigen und ausführen'
+    BUILDTASK_CAN_RUN_HELP: 'Darf alle /dev/tasks anzeigen und ausführen (/dev/tasks). Dies kann noch durch individuelle Berechtigungen für die Tasks überschrieben werden'
   SilverStripe\Forms\CheckboxField:
     NOANSWER: Nein
     YESANSWER: Ja
@@ -42,6 +55,7 @@ de:
     CURRENT_PASSWORD_MISSING: 'Bitte geben Sie Ihr derzeitiges Passwort ein.'
     LOGGED_IN_ERROR: 'Sie müssen eingeloggt sein, um Ihr Passwort ändern zu können!'
     MAXIMUM: 'Passwörter dürfen maximal {max} Zeichen lang sein.'
+    RANDOM_IF_EMPTY: 'Wenn dieses Feld leer gelassen wird, wird automatisch ein Zufallspasswort generiert.'
     SHOWONCLICKTITLE: 'Passwort ändern'
   SilverStripe\Forms\DateField:
     NOTSET: 'Nicht gesetzt'
@@ -103,7 +117,7 @@ de:
     Create: Erstellen
     Delete: Löschen
     DeletePermissionsFailure: 'Keine Berechtigungen zum löschen'
-    Deleted: 'Gelöscht {type} {name}'
+    Deleted: 'Gelöscht {type} "{name}"'
     Save: Speichern
     Saved: '{name} {link} gespeichert'
   SilverStripe\Forms\GridField\GridFieldDetailForm_ItemRequest:
@@ -111,6 +125,8 @@ de:
     NEW: 'Neuen Eintrag hinzufügen'
     NEXT: 'Gehe zu nächstem Eintrag'
     PREVIOUS: 'Gehe zu vorherigem Eintrag'
+    SAVEDUP: 'Erfolgreich gespeichert'
+    SAVETOASTMESSAGE: '{type} "{title}" erfolgreich gespeichert.'
     ViewPermissionsFailure: 'Sie haben nicht die nötigen Berechtigungen um {ObjectTitle} aufzurufen.'
   SilverStripe\Forms\GridField\GridFieldEditButton:
     EDIT: Bearbeiten
@@ -138,6 +154,10 @@ de:
     IsNullLabel: 'ist NULL'
   SilverStripe\Forms\NumericField:
     VALIDATION: "'{value}' ist kein numerischer Wert, nur nummerische Werte sind in diesem Feld erlaubt"
+  SilverStripe\Forms\SearchableDropdownTrait:
+    SELECT: Auswählen...
+    SELECT_OR_TYPE_TO_SEARCH: 'Auswählen oder tippen um zu suchen...'
+    TYPE_TO_SEARCH: 'Tippen um zu suchen...'
   SilverStripe\Forms\TextField:
     VALIDATEMAXLENGTH: 'Der für {name} eingegebene Wert darf nicht mehr als {maxLength} Zeichen lang sein'
   SilverStripe\Forms\TimeField:
@@ -145,11 +165,14 @@ de:
   SilverStripe\Forms\UrlField:
     INVALID: 'Bitte geben Sie eine gültige URL ein'
   SilverStripe\ORM\DataObject:
+    GENERALSEARCH: 'Generelle Suche'
     PLURALNAME: DatenObjekte
     PLURALS:
       one: 'Ein DatenObjekt'
       other: '{count} DatenObjekte'
     SINGULARNAME: DatenObjekt
+    many_many_FileTracking: Datei-Verfolgung
+    many_many_LinkTracking: Link-Verfolgung
   SilverStripe\ORM\FieldType\DBBoolean:
     ANY: alle
     NOANSWER: Nein
@@ -233,7 +256,11 @@ de:
     RolesAddEditLink: 'Rollen hinzufügen/editieren'
     SINGULARNAME: Gruppe
     Sort: Sortierreihenfolge
+    ValidationIdentifierAlreadyExists: 'Es existiert bereits eine Gruppe ({group}) mit dem selben {identifier}'
+    db_AccessAllSubsites: 'Zugang zu allen Unterseiten'
     db_Description: Beschreibung
+    db_LastSynced: 'Zuletzt aktualisiert'
+    db_Locked: Gesperrt
     db_Sort: Sortierung
     db_Title: Titel
     has_many_Groups: Gruppe
@@ -241,6 +268,13 @@ de:
     has_one_Parent: Übergeordnet
     many_many_Members: Mitglieder
     many_many_Roles: Rollen
+  SilverStripe\Security\InheritedPermissionsExtension:
+    db_CanEditType: 'Kann Typ bearbeiten'
+    db_CanViewType: 'Kann Typ ansehen'
+    many_many_EditorGroups: Bearbeitungsgruppen
+    many_many_EditorMembers: Bearbeitungsnutzer
+    many_many_ViewerGroups: Betrachtergruppen
+    many_many_ViewerMembers: Betrachtungsnutzer
   SilverStripe\Security\LoginAttempt:
     Email: E-Mail-Adresse
     EmailHashed: 'E-Mail-Adresse (gehashed)'
@@ -263,6 +297,7 @@ de:
     CURRENT_PASSWORD: 'Derzeitiges Passwort'
     EDIT_PASSWORD: 'Neues Passwort'
     EMAIL: E-Mail
+    EMAIL_FAILED: 'Beim Versuch, Ihnen einen Link zum Zurücksetzen des Passworts per E-Mail zu schicken, ist ein Fehler aufgetreten.'
     EMPTYNEWPASSWORD: 'Das neue Passwort darf nicht leer sein. Bitte versuchen Sie es erneut.'
     ENTEREMAIL: 'Bitte geben Sie eine E-Mail-Adresse ein, um einen Link zum Zurücksetzen des Passworts zu erhalten.'
     ERRORLOCKEDOUT2: 'Ihr Zugang wurde auf Grund von einer unzulässig hohen Anzahl von falschen Zugangsversuchen gesperrt. Bitte versuchen Sie es in {count} Minuten noch einmal.'
@@ -281,6 +316,7 @@ de:
     PLURALS:
       one: 'Ein Mitglied'
       other: '{count}  Mitglieder'
+    RequiresPasswordChangeOnNextLogin: 'Erfordert Passwortänderung bei nächster Anmeldung'
     SINGULARNAME: Benutzer
     SUBJECTPASSWORDCHANGED: 'Ihr Passwort wurde geändert'
     SUBJECTPASSWORDRESET: 'Ihr Link zur Passwortrücksetzung'
@@ -290,15 +326,34 @@ de:
     ValidationIdentifierFailed: 'Das vorhandene Mitglied #{id} mit identischer Bezeichnung kann nicht überschrieben werden ({name} = {value}))'
     WELCOMEBACK: 'Hallo {firstname}. Schön, dass du wieder da bist'
     YOUROLDPASSWORD: 'Ihr altes Passwort'
+    belongs_many_many_BlogPosts: Blogbeiträge
     belongs_many_many_Groups: Gruppe
+    db_AccountResetExpired: 'Zurücksetzen des Kontos ist abgelaufen'
+    db_AccountResetHash: 'Hash zum zurücksetzen des Accounts'
+    db_AutoLoginExpired: 'Automatische Anmeldung abgelaufen'
+    db_AutoLoginHash: 'Hash für die automatische Anmeldung'
+    db_BlogProfileSummary: 'Zusammenfassung für das Blogprofil'
     db_Email: E-Mail
+    db_FailedLoginCount: 'Anzahl der fehlgeschlagenen Anmeldungen'
     db_FirstName: Vorname
+    db_HasSkippedMFARegistration: 'Hat die MFA-Registrierung übersprungen'
+    db_IsExpired: 'Ist abgelaufen'
+    db_LastSynced: 'Zuletzt aktualisiert'
     db_Locale: 'Interface Sprachumgebung'
     db_LockedOutUntil: 'Gesperrt bis'
     db_Password: Passwort
+    db_PasswordEncryption: Passwortverschlüsselung
     db_PasswordExpiry: 'Ablaufdatum des Passworts'
+    db_Salt: Salz
     db_Surname: Nachname
     db_URLSegment: URL-Segment
+    db_Username: Nutzername
+    has_many_LoggedPasswords: 'Protokollierte Passwörter'
+    has_many_LoginSessions: Login-Sitzungen
+    has_many_RegisteredMFAMethods: 'Registrierte MFA-Methoden'
+    has_one_AFile: 'Eine Datei'
+    has_one_AImage: 'Ein Bild'
+    has_one_BlogProfileImage: 'Blogprofil Bild'
   SilverStripe\Security\MemberAuthenticator\CMSMemberLoginForm:
     AUTHENTICATORNAME: 'CMS Benutzer Login Formular'
     BUTTONFORGOTPASSWORD: 'Passwort vergessen'
@@ -316,6 +371,8 @@ de:
       other: '{count} Benutzerpasswörter'
     SINGULARNAME: Benutzerpasswort
     db_Password: Passwort
+    db_PasswordEncryption: Passwortverschlüsselung
+    db_Salt: Salz
     has_one_Member: Benutzer
   SilverStripe\Security\PasswordValidator:
     LOWCHARSTRENGTH: 'Bitte erhöhen Sie die Sicherheit des Passworts, indem Sie auch einige der folgenden Zeichen verwenden: {chars}'
@@ -363,6 +420,8 @@ de:
     PLURALS:
       one: 'Ein Login Hash'
       other: '{count} Login Hashes'
+    db_DeviceID: 'Geräte ID'
+    db_ExpiryDate: Ablaufdatum
     has_one_Member: Benutzer
   SilverStripe\Security\Security:
     ALREADYLOGGEDIN: 'Sie haben keinen Zugriff auf diese Seite. Wenn Sie ein anderes Konto besitzen, mit dem Sie auf diese Seite zugreifen können, melden Sie sich bitte unten an.'
diff --git a/src/Control/Controller.php b/src/Control/Controller.php
index 5b94f0ad6..299ce72a7 100644
--- a/src/Control/Controller.php
+++ b/src/Control/Controller.php
@@ -680,6 +680,18 @@ class Controller extends RequestHandler implements TemplateGlobalProvider
      */
     public static function normaliseTrailingSlash(string $url): string
     {
+        // Do not normalise external urls
+        // Note that urls without a scheme such as "www.example.com" will be counted as a relative file
+        if (!Director::is_site_url($url)) {
+            return $url;
+        }
+
+        // Do not modify files
+        $extension = pathinfo(Director::makeRelative($url), PATHINFO_EXTENSION);
+        if ($extension) {
+            return $url;
+        }
+
         $querystring = null;
         $fragmentIdentifier = null;
 
@@ -694,14 +706,9 @@ class Controller extends RequestHandler implements TemplateGlobalProvider
 
         // Normlise trailing slash
         $shouldHaveTrailingSlash = Controller::config()->uninherited('add_trailing_slash');
-        if ($shouldHaveTrailingSlash
-            && !str_ends_with($url, '/')
-            && !preg_match('/^(.*)\.([^\/]*)$/', Director::makeRelative($url))
-        ) {
-            // Add trailing slash if enabled and url does not end with a file extension
+        if ($shouldHaveTrailingSlash && !str_ends_with($url, '/')) {
             $url .= '/';
         } elseif (!$shouldHaveTrailingSlash) {
-            // Remove trailing slash if it shouldn't be there
             $url = rtrim($url, '/');
         }
 
diff --git a/src/Control/Director.php b/src/Control/Director.php
index 8318e5dd6..119d4e746 100644
--- a/src/Control/Director.php
+++ b/src/Control/Director.php
@@ -821,7 +821,16 @@ class Director implements TemplateGlobalProvider
 
         // Allow extensions to weigh in
         $isSiteUrl = false;
-        static::singleton()->extend('updateIsSiteUrl', $isSiteUrl, $url);
+        // Not using static::singleton() here because it can break
+        // functional tests such as those in HTTPCacheControlIntegrationTest
+        // This happens because a singleton of Director is instantiating prior to tests being run,
+        // because Controller::normaliseTrailingSlash() is called during SapphireTest::setUp(),
+        // which in turn calls Director::is_site_url()
+        // For this specific use case we don't need to use dependency injection because the
+        // chance of the extend() method being customised in projects is low.
+        // Any extension hooks implementing updateIsSiteUrl() will still be called as expected
+        $director = new static();
+        $director->extend('updateIsSiteUrl', $isSiteUrl, $url);
         if ($isSiteUrl) {
             return true;
         }
diff --git a/src/Forms/HTMLEditor/TinyMCEConfig.php b/src/Forms/HTMLEditor/TinyMCEConfig.php
index 297554024..73be7dd79 100644
--- a/src/Forms/HTMLEditor/TinyMCEConfig.php
+++ b/src/Forms/HTMLEditor/TinyMCEConfig.php
@@ -750,6 +750,7 @@ class TinyMCEConfig extends HTMLEditorConfig implements i18nEntityProvider
             }
 
             if (isset($preset['i18n'])) {
+                /** @phpstan-ignore translation.key (we need the key to be dynamic here) */
                 $preset['text'] = _t(
                     $preset['i18n'],
                     isset($preset['text']) ? $preset['text'] : ''
diff --git a/src/Forms/SearchableDropdownTrait.php b/src/Forms/SearchableDropdownTrait.php
index 2f6014d0d..83a9a0bc1 100644
--- a/src/Forms/SearchableDropdownTrait.php
+++ b/src/Forms/SearchableDropdownTrait.php
@@ -29,7 +29,7 @@ trait SearchableDropdownTrait
         'search',
     ];
 
-    private bool $isClearable = false;
+    private bool $isClearable = true;
 
     private bool $isLazyLoaded = false;
 
diff --git a/src/Forms/SearchableMultiDropdownField.php b/src/Forms/SearchableMultiDropdownField.php
index 3fe8f8c0a..90608a40d 100644
--- a/src/Forms/SearchableMultiDropdownField.php
+++ b/src/Forms/SearchableMultiDropdownField.php
@@ -24,6 +24,5 @@ class SearchableMultiDropdownField extends MultiSelectField
         $this->setLabelField($labelField);
         $this->addExtraClass('ss-searchable-dropdown-field');
         $this->setIsMultiple(true);
-        $this->setIsClearable(true);
     }
 }
diff --git a/src/ORM/Connect/MySQLDatabase.php b/src/ORM/Connect/MySQLDatabase.php
index 0aeb6067f..8e9e05851 100644
--- a/src/ORM/Connect/MySQLDatabase.php
+++ b/src/ORM/Connect/MySQLDatabase.php
@@ -566,6 +566,26 @@ class MySQLDatabase extends Database implements TransactionManager
      */
     public function clearTable($table)
     {
-        $this->query("TRUNCATE TABLE \"$table\"");
+        // Not simply using "TRUNCATE TABLE \"$table\"" because DELETE is a lot quicker
+        // than TRUNCATE which is very relevant during unit testing. Using TRUNCATE will lead to an
+        // approximately 50% increase it the total time of running unit tests.
+        //
+        // Using max(ID) to determine if the table should reset its auto-increment, rather than using
+        // SELECT "AUTO_INCREMENT" FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_SCHEMA = ? AND TABLE_NAME = ?
+        // after deleting from the table, because in MySQL 8, under certain conditions, notably
+        // when running behat, sometimes the auto-increment was being reset to 2 for unknown reasons
+        $self = $this;
+        $fn = function () use ($self, $table) {
+            $maxID = $self->query("SELECT MAX(ID) FROM \"$table\"")->value();
+            $self->query("DELETE FROM \"$table\"");
+            if ($maxID > 0) {
+                $self->query("ALTER TABLE \"$table\" AUTO_INCREMENT = 1");
+            }
+        };
+        if ($this->supportsTransactions()) {
+            $this->withTransaction($fn);
+        } else {
+            $fn();
+        }
     }
 }
diff --git a/src/ORM/DataObject.php b/src/ORM/DataObject.php
index 86ddce770..aa687ae24 100644
--- a/src/ORM/DataObject.php
+++ b/src/ORM/DataObject.php
@@ -3959,6 +3959,7 @@ class DataObject extends ViewableData implements DataObjectInterface, i18nEntity
                     }
                     foreach ($types as $type => $attrs) {
                         foreach ($attrs as $name => $spec) {
+                            /** @phpstan-ignore translation.key (we need the key to be dynamic here) */
                             $autoLabels[$name] = _t(
                                 "{$ancestorClass}.{$type}_{$name}",
                                 FormField::name_to_label($name)
diff --git a/src/Security/PasswordValidator.php b/src/Security/PasswordValidator.php
index 179711877..62288201d 100644
--- a/src/Security/PasswordValidator.php
+++ b/src/Security/PasswordValidator.php
@@ -203,6 +203,7 @@ class PasswordValidator
                 if (preg_match($tests[$name] ?? '', $password ?? '')) {
                     continue;
                 }
+                /** @phpstan-ignore translation.key (we need the key to be dynamic here) */
                 $missedTests[] = _t(
                     __CLASS__ . '.STRENGTHTEST' . strtoupper($name ?? ''),
                     $name,
diff --git a/tests/php/Control/ControllerTest.php b/tests/php/Control/ControllerTest.php
index ee1222dda..29d520eb6 100644
--- a/tests/php/Control/ControllerTest.php
+++ b/tests/php/Control/ControllerTest.php
@@ -276,14 +276,17 @@ class ControllerTest extends FunctionalTest
     {
         /* Controller::join_links() will reliably join two URL-segments together so that they will be
         * appropriately parsed by the URL parser */
+        Director::config()->set('alternate_base_url', 'https://www.internal.com');
         Controller::config()->set('add_trailing_slash', false);
         $this->assertEquals("admin/crm/MyForm", Controller::join_links("admin/crm", "MyForm"));
         $this->assertEquals("admin/crm/MyForm", Controller::join_links("admin/crm/", "MyForm"));
-        $this->assertEquals("https://www.test.com/admin/crm/MyForm", Controller::join_links("https://www.test.com", "admin/crm/", "MyForm"));
+        $this->assertEquals("https://www.internal.com/admin/crm/MyForm", Controller::join_links("https://www.internal.com", "admin/crm/", "MyForm"));
+        $this->assertEquals("https://www.external.com/admin/crm/MyForm", Controller::join_links("https://www.external.com", "admin/crm/", "MyForm"));
         Controller::config()->set('add_trailing_slash', true);
         $this->assertEquals("admin/crm/MyForm/", Controller::join_links("admin/crm", "MyForm"));
         $this->assertEquals("admin/crm/MyForm/", Controller::join_links("admin/crm/", "MyForm"));
-        $this->assertEquals("https://www.test.com/admin/crm/MyForm/", Controller::join_links("https://www.test.com", "admin/crm/", "MyForm"));
+        $this->assertEquals("https://www.internal.com/admin/crm/MyForm/", Controller::join_links("https://www.internal.com", "admin/crm/", "MyForm"));
+        $this->assertEquals("https://www.external.com/admin/crm/MyForm", Controller::join_links("https://www.external.com", "admin/crm/", "MyForm"));
 
         /* It will also handle appropriate combination of querystring variables */
         Controller::config()->set('add_trailing_slash', false);
@@ -293,7 +296,8 @@ class ControllerTest extends FunctionalTest
             "admin/crm/MyForm?field=1&other=1",
             Controller::join_links("admin/crm/?field=1", "MyForm?other=1")
         );
-        $this->assertEquals("https://www.test.com/admin/crm/MyForm?flush=1", Controller::join_links("https://www.test.com", "admin/crm/", "MyForm?flush=1"));
+        $this->assertEquals("https://www.internal.com/admin/crm/MyForm?flush=1", Controller::join_links("https://www.internal.com", "admin/crm/", "MyForm?flush=1"));
+        $this->assertEquals("https://www.external.com/admin/crm/MyForm?flush=1", Controller::join_links("https://www.external.com", "admin/crm/", "MyForm?flush=1"));
         Controller::config()->set('add_trailing_slash', true);
         $this->assertEquals("admin/crm/MyForm/?flush=1", Controller::join_links("admin/crm/?flush=1", "MyForm"));
         $this->assertEquals("admin/crm/MyForm/?flush=1", Controller::join_links("admin/crm/", "MyForm?flush=1"));
@@ -301,7 +305,8 @@ class ControllerTest extends FunctionalTest
             "admin/crm/MyForm/?field=1&other=1",
             Controller::join_links("admin/crm/?field=1", "MyForm?other=1")
         );
-        $this->assertEquals("https://www.test.com/admin/crm/MyForm/?flush=1", Controller::join_links("https://www.test.com", "admin/crm/", "MyForm?flush=1"));
+        $this->assertEquals("https://www.internal.com/admin/crm/MyForm/?flush=1", Controller::join_links("https://www.internal.com", "admin/crm/", "MyForm?flush=1"));
+        $this->assertEquals("https://www.external.com/admin/crm/MyForm?flush=1", Controller::join_links("https://www.external.com", "admin/crm/", "MyForm?flush=1"));
 
         /* It can handle arbitrary numbers of components, and will ignore empty ones */
         Controller::config()->set('add_trailing_slash', false);
@@ -340,8 +345,12 @@ class ControllerTest extends FunctionalTest
             Controller::join_links("admin/crm?foo=1&bar=1&baz=1", "?foo=2&bar=3")
         );
         $this->assertEquals(
-            "https://www.test.com/admin/crm?foo=2&bar=3&baz=1",
-            Controller::join_links("https://www.test.com", "admin/crm?foo=1&bar=1&baz=1", "?foo=2&bar=3")
+            "https://www.internal.com/admin/crm?foo=2&bar=3&baz=1",
+            Controller::join_links("https://www.internal.com", "admin/crm?foo=1&bar=1&baz=1", "?foo=2&bar=3")
+        );
+        $this->assertEquals(
+            "https://www.external.com/admin/crm?foo=2&bar=3&baz=1",
+            Controller::join_links("https://www.external.com", "admin/crm?foo=1&bar=1&baz=1", "?foo=2&bar=3")
         );
         Controller::config()->set('add_trailing_slash', true);
         $this->assertEquals(
@@ -349,8 +358,12 @@ class ControllerTest extends FunctionalTest
             Controller::join_links("admin/crm?foo=1&bar=1&baz=1", "?foo=2&bar=3")
         );
         $this->assertEquals(
-            "https://www.test.com/admin/crm/?foo=2&bar=3&baz=1",
-            Controller::join_links("https://www.test.com", "admin/crm?foo=1&bar=1&baz=1", "?foo=2&bar=3")
+            "https://www.internal.com/admin/crm/?foo=2&bar=3&baz=1",
+            Controller::join_links("https://www.internal.com", "admin/crm?foo=1&bar=1&baz=1", "?foo=2&bar=3")
+        );
+        $this->assertEquals(
+            "https://www.external.com/admin/crm?foo=2&bar=3&baz=1",
+            Controller::join_links("https://www.external.com", "admin/crm?foo=1&bar=1&baz=1", "?foo=2&bar=3")
         );
 
         Controller::config()->set('add_trailing_slash', false);
@@ -361,8 +374,13 @@ class ControllerTest extends FunctionalTest
         );
         $this->assertEquals('/admin/action', Controller::join_links('/admin', 'action'));
         $this->assertEquals(
-            'https://www.test.com/admin/action',
-            Controller::join_links('https://www.test.com', '/', '/admin/', '/', '/action'),
+            'https://www.internal.com/admin/action',
+            Controller::join_links('https://www.internal.com', '/', '/admin/', '/', '/action'),
+            'Test that multiple slashes are trimmed.'
+        );
+        $this->assertEquals(
+            'https://www.external.com/admin/action',
+            Controller::join_links('https://www.external.com', '/', '/admin/', '/', '/action'),
             'Test that multiple slashes are trimmed.'
         );
         Controller::config()->set('add_trailing_slash', true);
@@ -373,8 +391,13 @@ class ControllerTest extends FunctionalTest
         );
         $this->assertEquals('/admin/action/', Controller::join_links('/admin', 'action'));
         $this->assertEquals(
-            'https://www.test.com/admin/action/',
-            Controller::join_links('https://www.test.com', '/', '/admin/', '/', '/action'),
+            'https://www.internal.com/admin/action/',
+            Controller::join_links('https://www.internal.com', '/', '/admin/', '/', '/action'),
+            'Test that multiple slashes are trimmed.'
+        );
+        $this->assertEquals(
+            'https://www.external.com/admin/action',
+            Controller::join_links('https://www.external.com', '/', '/admin/', '/', '/action'),
             'Test that multiple slashes are trimmed.'
         );
 
@@ -391,8 +414,12 @@ class ControllerTest extends FunctionalTest
             Controller::join_links("my-page#subsection", "?arg=var", "#second-section")
         );
         $this->assertEquals(
-            "https://www.test.com/my-page?arg=var#second-section",
-            Controller::join_links("https://www.test.com", "my-page#subsection", "?arg=var", "#second-section")
+            "https://www.internal.com/my-page?arg=var#second-section",
+            Controller::join_links("https://www.internal.com", "my-page#subsection", "?arg=var", "#second-section")
+        );
+        $this->assertEquals(
+            "https://www.external.com/my-page?arg=var#second-section",
+            Controller::join_links("https://www.external.com", "my-page#subsection", "?arg=var", "#second-section")
         );
         Controller::config()->set('add_trailing_slash', true);
         $this->assertEquals(
@@ -400,8 +427,12 @@ class ControllerTest extends FunctionalTest
             Controller::join_links("my-page#subsection", "?arg=var", "#second-section")
         );
         $this->assertEquals(
-            "https://www.test.com/my-page/?arg=var#second-section",
-            Controller::join_links("https://www.test.com", "my-page#subsection", "?arg=var", "#second-section")
+            "https://www.internal.com/my-page/?arg=var#second-section",
+            Controller::join_links("https://www.internal.com", "my-page#subsection", "?arg=var", "#second-section")
+        );
+        $this->assertEquals(
+            "https://www.external.com/my-page?arg=var#second-section",
+            Controller::join_links("https://www.external.com", "my-page#subsection", "?arg=var", "#second-section")
         );
 
         /* Does type-safe checks for zero value */
@@ -413,60 +444,245 @@ class ControllerTest extends FunctionalTest
         // Test array args
         Controller::config()->set('add_trailing_slash', false);
         $this->assertEquals(
-            "https://www.test.com/admin/crm/MyForm?a=1&b=2&c=3",
-            Controller::join_links(["https://www.test.com", "?a=1", "admin/crm", "?b=2", "MyForm?c=3"])
+            "https://www.internal.com/admin/crm/MyForm?a=1&b=2&c=3",
+            Controller::join_links(["https://www.internal.com", "?a=1", "admin/crm", "?b=2", "MyForm?c=3"])
+        );
+        $this->assertEquals(
+            "https://www.external.com/admin/crm/MyForm?a=1&b=2&c=3",
+            Controller::join_links(["https://www.external.com", "?a=1", "admin/crm", "?b=2", "MyForm?c=3"])
         );
         Controller::config()->set('add_trailing_slash', true);
         $this->assertEquals(
-            "https://www.test.com/admin/crm/MyForm/?a=1&b=2&c=3",
-            Controller::join_links(["https://www.test.com", "?a=1", "admin/crm", "?b=2", "MyForm?c=3"])
+            "https://www.internal.com/admin/crm/MyForm/?a=1&b=2&c=3",
+            Controller::join_links(["https://www.internal.com", "?a=1", "admin/crm", "?b=2", "MyForm?c=3"])
+        );
+        $this->assertEquals(
+            "https://www.external.com/admin/crm/MyForm?a=1&b=2&c=3",
+            Controller::join_links(["https://www.external.com", "?a=1", "admin/crm", "?b=2", "MyForm?c=3"])
         );
     }
 
-    public function testNormaliseTrailingSlash()
+    public function provideNormaliseTrailingSlash(): array
     {
-        foreach ([true, false] as $withTrailingSlash) {
-            Controller::config()->set('add_trailing_slash', $withTrailingSlash);
-            $slash = $withTrailingSlash ? '/' : '';
-
+        // note 93.184.215.14 is the IP address for example.com
+        return [
             // Correctly gives slash to a relative root path
-            $this->assertEquals('/', Controller::normaliseTrailingSlash(''));
-            $this->assertEquals('/', Controller::normaliseTrailingSlash('/'));
-
+            [
+                'path' => '',
+                'withSlash' => '/',
+                'withoutSlash' => '/',
+            ],
+            [
+                'path' => '/',
+                'withSlash' => '/',
+                'withoutSlash' => '/',
+            ],
             // Correctly adds or removes trailing slash
-            $this->assertEquals("some/path{$slash}", Controller::normaliseTrailingSlash('some/path/'));
-            $this->assertEquals("some/path{$slash}", Controller::normaliseTrailingSlash('some/path'));
-
+            [
+                'path' => 'some/path/',
+                'withSlash' => 'some/path/',
+                'withoutSlash' => 'some/path',
+            ],
             // Retains leading slash, if there is one
-            $this->assertEquals("/some/path{$slash}", Controller::normaliseTrailingSlash('/some/path/'));
-            $this->assertEquals("/some/path{$slash}", Controller::normaliseTrailingSlash('/some/path'));
-
-            // Effectively treats absolute URL as relative
-            $this->assertEquals("https://www.google.com/some/path{$slash}", Controller::normaliseTrailingSlash('https://www.google.com/some/path/'));
-            $this->assertEquals("//www.google.com/some/path{$slash}", Controller::normaliseTrailingSlash('//www.google.com/some/path'));
-            $this->assertEquals("www.google.com/some/path{$slash}", Controller::normaliseTrailingSlash('www.google.com/some/path'));
-            $this->assertEquals("https://www.google.com{$slash}", Controller::normaliseTrailingSlash('https://www.google.com'));
-            $this->assertEquals("//www.google.com{$slash}", Controller::normaliseTrailingSlash('//www.google.com/'));
-
+            [
+                'path' => '/some/path/',
+                'withSlash' => '/some/path/',
+                'withoutSlash' => '/some/path',
+            ],
+            // Treat absolute URLs pointing to the current site as relative
+            [
+                'path' => '<AbsoluteBaseUrl>/some/path/',
+                'withSlash' => '<AbsoluteBaseUrl>/some/path/',
+                'withoutSlash' => '<AbsoluteBaseUrl>/some/path',
+            ],
+            [
+                'path' => '<AbsoluteBaseUrl>/',
+                'withSlash' => '<AbsoluteBaseUrl>/',
+                'withoutSlash' => '<AbsoluteBaseUrl>',
+            ],
+            [
+                'path' => '<AbsoluteBaseUrl>',
+                'withSlash' => '<AbsoluteBaseUrl>/',
+                'withoutSlash' => '<AbsoluteBaseUrl>',
+            ],
+            // External links never get normalised
+            [
+                'path' => 'https://www.example.com/some/path',
+                'withSlash' => 'https://www.example.com/some/path',
+                'withoutSlash' => 'https://www.example.com/some/path',
+            ],
+            [
+                'path' => 'https://www.example.com/some/path/',
+                'withSlash' => 'https://www.example.com/some/path/',
+                'withoutSlash' => 'https://www.example.com/some/path/',
+            ],
+            [
+                'path' => 'https://www.example.com',
+                'withSlash' => 'https://www.example.com',
+                'withoutSlash' => 'https://www.example.com',
+            ],
+            [
+                'path' => 'https://www.example.com/',
+                'withSlash' => 'https://www.example.com/',
+                'withoutSlash' => 'https://www.example.com/',
+            ],
+            [
+                'path' => '//www.example.com/some/path',
+                'withSlash' => '//www.example.com/some/path',
+                'withoutSlash' => '//www.example.com/some/path',
+            ],
+            [
+                'path' => '//www.example.com/some/path/',
+                'withSlash' => '//www.example.com/some/path/',
+                'withoutSlash' => '//www.example.com/some/path/',
+            ],
+            [
+                'path' => '//www.example.com',
+                'withSlash' => '//www.example.com',
+                'withoutSlash' => '//www.example.com',
+            ],
+            [
+                'path' => '//www.example.com/',
+                'withSlash' => '//www.example.com/',
+                'withoutSlash' => '//www.example.com/',
+            ],
+            [
+                'path' => 'https://93.184.215.14/some/path',
+                'withSlash' => 'https://93.184.215.14/some/path',
+                'withoutSlash' => 'https://93.184.215.14/some/path',
+            ],
+            [
+                'path' => 'https://93.184.215.14/some/path/',
+                'withSlash' => 'https://93.184.215.14/some/path/',
+                'withoutSlash' => 'https://93.184.215.14/some/path/',
+            ],
+            // Links without a scheme with a path are treated as relative
+            // Note: content authors should be specifying a scheme in these cases themselves
+            [
+                'path' => 'www.example.com/some/path',
+                'withSlash' => 'www.example.com/some/path/',
+                'withoutSlash' => 'www.example.com/some/path',
+            ],
+            [
+                'path' => 'www.example.com/some/path/',
+                'withSlash' => 'www.example.com/some/path/',
+                'withoutSlash' => 'www.example.com/some/path',
+            ],
+            [
+                'path' => '93.184.215.14/some/path',
+                'withSlash' => '93.184.215.14/some/path/',
+                'withoutSlash' => '93.184.215.14/some/path',
+            ],
+            [
+                'path' => '93.184.215.14/some/path/',
+                'withSlash' => '93.184.215.14/some/path/',
+                'withoutSlash' => '93.184.215.14/some/path',
+            ],
+            // Links without a scheme or path are treated like files i.e. not altered
+            // Note: content authors should be specifying a scheme in these cases themselves
+            [
+                'path' => 'www.example.com',
+                'withSlash' => 'www.example.com',
+                'withoutSlash' => 'www.example.com',
+            ],
+            [
+                'path' => 'www.example.com/',
+                'withSlash' => 'www.example.com/',
+                'withoutSlash' => 'www.example.com/',
+            ],
+            [
+                'path' => '93.184.215.14',
+                'withSlash' => '93.184.215.14',
+                'withoutSlash' => '93.184.215.14',
+            ],
+            [
+                'path' => '93.184.215.14/',
+                'withSlash' => '93.184.215.14/',
+                'withoutSlash' => '93.184.215.14/',
+            ],
             // Retains query string and anchor if present
-            $this->assertEquals("some/path{$slash}?key=value&key2=value2", Controller::normaliseTrailingSlash('some/path/?key=value&key2=value2'));
-            $this->assertEquals("some/path{$slash}#some-id", Controller::normaliseTrailingSlash('some/path/#some-id'));
-            $this->assertEquals("some/path{$slash}?key=value&key2=value2#some-id", Controller::normaliseTrailingSlash('some/path/?key=value&key2=value2#some-id'));
-            $this->assertEquals("some/path{$slash}?key=value&key2=value2", Controller::normaliseTrailingSlash('some/path?key=value&key2=value2'));
-            $this->assertEquals("some/path{$slash}#some-id", Controller::normaliseTrailingSlash('some/path#some-id'));
-            $this->assertEquals("some/path{$slash}?key=value&key2=value2#some-id", Controller::normaliseTrailingSlash('some/path?key=value&key2=value2#some-id'));
-
+            [
+                'path' => 'some/path/?key=value&key2=value2',
+                'withSlash' => 'some/path/?key=value&key2=value2',
+                'withoutSlash' => 'some/path?key=value&key2=value2',
+            ],
+            [
+                'path' => 'some/path/#some-id',
+                'withSlash' => 'some/path/#some-id',
+                'withoutSlash' => 'some/path#some-id',
+            ],
+            [
+                'path' => 'some/path?key=value&key2=value2#some-id',
+                'withSlash' => 'some/path/?key=value&key2=value2#some-id',
+                'withoutSlash' => 'some/path?key=value&key2=value2#some-id',
+            ],
+            [
+                'path' => 'some/path?key=value&key2=value2',
+                'withSlash' => 'some/path/?key=value&key2=value2',
+                'withoutSlash' => 'some/path?key=value&key2=value2',
+            ],
+            [
+                'path' => 'some/path#some-id',
+                'withSlash' => 'some/path/#some-id',
+                'withoutSlash' => 'some/path#some-id',
+            ],
+            [
+                'path' => 'some/path?key=value&key2=value2#some-id',
+                'withSlash' => 'some/path/?key=value&key2=value2#some-id',
+                'withoutSlash' => 'some/path?key=value&key2=value2#some-id',
+            ],
             // Don't ever add a trailing slash to the end of a URL that looks like a file
-            $this->assertEquals("https://www.google.com/some/file.txt", Controller::normaliseTrailingSlash('https://www.google.com/some/file.txt'));
-            $this->assertEquals("//www.google.com/some/file.txt", Controller::normaliseTrailingSlash('//www.google.com/some/file.txt'));
-            $this->assertEquals("www.google.com/some/file.txt", Controller::normaliseTrailingSlash('www.google.com/some/file.txt'));
-            $this->assertEquals("/some/file.txt", Controller::normaliseTrailingSlash('/some/file.txt'));
-            $this->assertEquals("some/file.txt", Controller::normaliseTrailingSlash('some/file.txt'));
-            $this->assertEquals("file.txt", Controller::normaliseTrailingSlash('file.txt'));
-            $this->assertEquals("some/file.txt?key=value&key2=value2#some-id", Controller::normaliseTrailingSlash('some/file.txt?key=value&key2=value2#some-id'));
-            // NOTE: `www.google.com` is already treated as "relative" by Director::makeRelative(), which means we can't tell that it's a host (and not a file).
-            $this->assertEquals("www.google.com", Controller::normaliseTrailingSlash('www.google.com'));
-        }
+            [
+                'path' => 'https://www.example.com/some/file.txt',
+                'withSlash' => 'https://www.example.com/some/file.txt',
+                'withoutSlash' => 'https://www.example.com/some/file.txt',
+            ],
+            [
+                'path' => '//www.example.com/some/file.txt',
+                'withSlash' => '//www.example.com/some/file.txt',
+                'withoutSlash' => '//www.example.com/some/file.txt',
+            ],
+            [
+                'path' => 'www.example.com/some/file.txt',
+                'withSlash' => 'www.example.com/some/file.txt',
+                'withoutSlash' => 'www.example.com/some/file.txt',
+            ],
+            [
+                'path' => '/some/file.txt',
+                'withSlash' => '/some/file.txt',
+                'withoutSlash' => '/some/file.txt',
+            ],
+            [
+                'path' => 'some/file.txt',
+                'withSlash' => 'some/file.txt',
+                'withoutSlash' => 'some/file.txt',
+            ],
+            [
+                'path' => 'file.txt',
+                'withSlash' => 'file.txt',
+                'withoutSlash' => 'file.txt',
+            ],
+            [
+                'path' => 'some/file.txt?key=value&key2=value2#some-id',
+                'withSlash' => 'some/file.txt?key=value&key2=value2#some-id',
+                'withoutSlash' => 'some/file.txt?key=value&key2=value2#some-id',
+            ],
+        ];
+    }
+
+    /**
+     * @dataProvider provideNormaliseTrailingSlash
+     */
+    public function testNormaliseTrailingSlash(string $path, string $withSlash, string $withoutSlash): void
+    {
+        $absBaseUrlNoSlash = rtrim(Director::absoluteBaseURL(), '/');
+        $path = str_replace('<AbsoluteBaseUrl>', $absBaseUrlNoSlash, $path);
+        $withSlash = str_replace('<AbsoluteBaseUrl>', $absBaseUrlNoSlash, $withSlash);
+        $withoutSlash = str_replace('<AbsoluteBaseUrl>', $absBaseUrlNoSlash, $withoutSlash);
+        Controller::config()->set('add_trailing_slash', true);
+        $this->assertEquals($withSlash, Controller::normaliseTrailingSlash($path), 'With trailing slash test');
+        Controller::config()->set('add_trailing_slash', false);
+        $this->assertEquals($withoutSlash, Controller::normaliseTrailingSlash($path), 'Without trailing slash test');
     }
 
     public function testLink()
diff --git a/tests/php/Control/DirectorTest.php b/tests/php/Control/DirectorTest.php
index f0332322e..1c65b5bb3 100644
--- a/tests/php/Control/DirectorTest.php
+++ b/tests/php/Control/DirectorTest.php
@@ -109,21 +109,21 @@ class DirectorTest extends SapphireTest
 
             // Test Director::BASE
             $this->assertEquals("http://www.mysite.com:9090{$slash}", Director::absoluteURL('http://www.mysite.com:9090/', Director::BASE));
-            $this->assertEquals("http://www.mytest.com{$slash}", Director::absoluteURL('http://www.mytest.com', Director::BASE));
+            $this->assertEquals("http://www.mytest.com", Director::absoluteURL('http://www.mytest.com', Director::BASE));
             $this->assertEquals("http://www.mysite.com:9090/test{$slash}", Director::absoluteURL("http://www.mysite.com:9090/test", Director::BASE));
             $this->assertEquals("http://www.mysite.com:9090/root{$slash}", Director::absoluteURL("/root", Director::BASE));
             $this->assertEquals("http://www.mysite.com:9090/root/url{$slash}", Director::absoluteURL("/root/url", Director::BASE));
 
             // Test Director::ROOT
             $this->assertEquals("http://www.mysite.com:9090{$slash}", Director::absoluteURL('http://www.mysite.com:9090/', Director::ROOT));
-            $this->assertEquals("http://www.mytest.com{$slash}", Director::absoluteURL('http://www.mytest.com', Director::ROOT));
+            $this->assertEquals("http://www.mytest.com", Director::absoluteURL('http://www.mytest.com', Director::ROOT));
             $this->assertEquals("http://www.mysite.com:9090/test{$slash}", Director::absoluteURL("http://www.mysite.com:9090/test", Director::ROOT));
             $this->assertEquals("http://www.mysite.com:9090/root{$slash}", Director::absoluteURL("/root", Director::ROOT));
             $this->assertEquals("http://www.mysite.com:9090/root/url{$slash}", Director::absoluteURL("/root/url", Director::ROOT));
 
             // Test Director::REQUEST
             $this->assertEquals("http://www.mysite.com:9090{$slash}", Director::absoluteURL('http://www.mysite.com:9090/', Director::REQUEST));
-            $this->assertEquals("http://www.mytest.com{$slash}", Director::absoluteURL('http://www.mytest.com', Director::REQUEST));
+            $this->assertEquals("http://www.mytest.com", Director::absoluteURL('http://www.mytest.com', Director::REQUEST));
             $this->assertEquals("http://www.mysite.com:9090/test{$slash}", Director::absoluteURL("http://www.mysite.com:9090/test", Director::REQUEST));
             $this->assertEquals("http://www.mysite.com:9090/root{$slash}", Director::absoluteURL("/root", Director::REQUEST));
             $this->assertEquals("http://www.mysite.com:9090/root/url{$slash}", Director::absoluteURL("/root/url", Director::REQUEST));
diff --git a/tests/php/Control/Middleware/CanonicalURLMiddlewareTest.php b/tests/php/Control/Middleware/CanonicalURLMiddlewareTest.php
index 5689fb767..2770874ab 100644
--- a/tests/php/Control/Middleware/CanonicalURLMiddlewareTest.php
+++ b/tests/php/Control/Middleware/CanonicalURLMiddlewareTest.php
@@ -8,6 +8,7 @@ use SilverStripe\Control\HTTPResponse;
 use SilverStripe\Control\Middleware\CanonicalURLMiddleware;
 use SilverStripe\Core\Environment;
 use SilverStripe\Dev\SapphireTest;
+use SilverStripe\Control\Director;
 
 class CanonicalURLMiddlewareTest extends SapphireTest
 {
@@ -121,6 +122,7 @@ class CanonicalURLMiddlewareTest extends SapphireTest
 
     private function performRedirectTest(string $requestURL, CanonicalURLMiddleware $middleware, bool $shouldRedirect, bool $addTrailingSlash)
     {
+        Director::config()->set('alternate_base_url', 'https://www.example.com');
         Environment::setEnv('REQUEST_URI', $requestURL);
         $request = new HTTPRequest('GET', $requestURL);
         $request->setScheme('https');
diff --git a/tests/php/Forms/SearchableDropdownTraitTest.php b/tests/php/Forms/SearchableDropdownTraitTest.php
index 7f4858c81..d3796cfa2 100644
--- a/tests/php/Forms/SearchableDropdownTraitTest.php
+++ b/tests/php/Forms/SearchableDropdownTraitTest.php
@@ -205,16 +205,16 @@ class SearchableDropdownTraitTest extends SapphireTest
         $field->setForm($form);
         $schema = $field->getSchemaDataDefaults();
         $this->assertFalse($schema['lazyLoad']);
-        $this->assertFalse($schema['clearable']);
+        $this->assertTrue($schema['clearable']);
         $this->assertSame('Select or type to search...', $schema['placeholder']);
         $this->assertTrue($schema['searchable']);
         $field->setIsLazyLoaded(true);
-        $field->setIsClearable(true);
+        $field->setIsClearable(false);
         $field->setPlaceholder('My placeholder');
         $field->setIsSearchable(false);
         $schema = $field->getSchemaDataDefaults();
         $this->assertTrue($schema['lazyLoad']);
-        $this->assertTrue($schema['clearable']);
+        $this->assertFalse($schema['clearable']);
         $this->assertSame('My placeholder', $schema['placeholder']);
         $this->assertFalse($schema['searchable']);
     }