diff --git a/typo3/sysext/backend/Classes/Controller/BackendController.php b/typo3/sysext/backend/Classes/Controller/BackendController.php
index 070cd4ac7c53b14efad88edbf34e61b0e3b3847c..e1019d2fcc5139aef645fc98d6ae858083b8b971 100644
--- a/typo3/sysext/backend/Classes/Controller/BackendController.php
+++ b/typo3/sysext/backend/Classes/Controller/BackendController.php
@@ -582,7 +582,6 @@ class BackendController
             'pageModule' => $pageModule,
             'inWorkspace' => $beUser->workspace !== 0,
             'showRefreshLoginPopup' => isset($GLOBALS['TYPO3_CONF_VARS']['BE']['showRefreshLoginPopup']) ? (int)$GLOBALS['TYPO3_CONF_VARS']['BE']['showRefreshLoginPopup'] : false,
-            'debugInWindow' => $beUser->uc['debugInWindow'] ? 1 : 0,
             'ContextHelpWindows' => [
                 'width' => 600,
                 'height' => 400
diff --git a/typo3/sysext/core/Documentation/Changelog/master/Breaking-78522-RemoveBackendUserOptionDebugInWindow.rst b/typo3/sysext/core/Documentation/Changelog/master/Breaking-78522-RemoveBackendUserOptionDebugInWindow.rst
new file mode 100644
index 0000000000000000000000000000000000000000..85e583c724fc678911b51d796999630c6c1d4644
--- /dev/null
+++ b/typo3/sysext/core/Documentation/Changelog/master/Breaking-78522-RemoveBackendUserOptionDebugInWindow.rst
@@ -0,0 +1,26 @@
+.. include:: ../../Includes.txt
+
+============================================================
+Breaking: #78522 - Removed backend user option debugInWindow
+============================================================
+
+See :issue:`78522`
+
+Description
+===========
+
+The backend user option `debugInWindow` is unused in the core and has been removed,
+as the option of opening the debug information in a window was migrated already.
+
+Impact
+======
+
+The setting is not available anymore in JavaScript under :js:`TYPO3.configuration`.
+
+
+Affected Installations
+======================
+
+Any installation that uses the removed backend user option `debugInWindow`.
+
+.. index:: Backend, JavaScript
diff --git a/typo3/sysext/setup/Resources/Private/Language/locallang.xlf b/typo3/sysext/setup/Resources/Private/Language/locallang.xlf
index c81a61680f435a280098135ef0a6432787a9adbc..248fbfead7ebaf75a1dbd892b62329f0ffc04532 100644
--- a/typo3/sysext/setup/Resources/Private/Language/locallang.xlf
+++ b/typo3/sysext/setup/Resources/Private/Language/locallang.xlf
@@ -369,9 +369,6 @@
 			<trans-unit id="oldPassword_failed">
 				<source>Password was NOT updated because you didn't enter the correct current password.</source>
 			</trans-unit>
-			<trans-unit id="adminFunctions">
-				<source>Admin functions</source>
-			</trans-unit>
 			<trans-unit id="enableInstallTool.label">
 				<source>Install Tool Access</source>
 			</trans-unit>
@@ -402,9 +399,6 @@
 			<trans-unit id="settingsAreReset">
 				<source>The user settings have been reset to default values and temporary data has been cleared.</source>
 			</trans-unit>
-			<trans-unit id="debugInWindow">
-				<source>Display debug messages in a new browser window</source>
-			</trans-unit>
 			<trans-unit id="startModule.firstInMenu">
 				<source>- First module in menu -</source>
 			</trans-unit>
diff --git a/typo3/sysext/setup/ext_tables.php b/typo3/sysext/setup/ext_tables.php
index 98664d7d94de2d2aff9bd3445e6ea9ba7a2c33d0..00a17e367ca546b25221dd4b574ce76fe161ab18 100644
--- a/typo3/sysext/setup/ext_tables.php
+++ b/typo3/sysext/setup/ext_tables.php
@@ -131,16 +131,10 @@ if (TYPO3_MODE === 'BE') {
                 'label' => 'LLL:EXT:setup/Resources/Private/Language/locallang.xlf:flexibleTextareas_MaxHeight',
                 'csh' => 'flexibleTextareas_MaxHeight'
             ],
-            'debugInWindow' => [
-                'type' => 'check',
-                'label' => 'LLL:EXT:setup/Resources/Private/Language/locallang.xlf:debugInWindow',
-                'access' => 'admin'
-            ]
         ],
         'showitem' => '--div--;LLL:EXT:setup/Resources/Private/Language/locallang.xlf:personal_data,realName,email,emailMeAtLogin,avatar,lang,
 				--div--;LLL:EXT:setup/Resources/Private/Language/locallang.xml:passwordHeader,passwordCurrent,password,password2,
 				--div--;LLL:EXT:setup/Resources/Private/Language/locallang.xlf:opening,startModule,
-				--div--;LLL:EXT:setup/Resources/Private/Language/locallang.xlf:editFunctionsTab,edit_RTE,resizeTextareas_Flexible,resizeTextareas_MaxHeight,titleLen,thumbnailsByDefault,edit_docModuleUpload,showHiddenFilesAndFolders,copyLevels,recursiveDelete,resetConfiguration,
-				--div--;LLL:EXT:setup/Resources/Private/Language/locallang.xlf:adminFunctions,debugInWindow'
+				--div--;LLL:EXT:setup/Resources/Private/Language/locallang.xlf:editFunctionsTab,edit_RTE,resizeTextareas_Flexible,resizeTextareas_MaxHeight,titleLen,thumbnailsByDefault,edit_docModuleUpload,showHiddenFilesAndFolders,copyLevels,recursiveDelete,resetConfiguration'
     ];
 }
diff --git a/typo3/sysext/workspaces/Classes/Controller/PreviewController.php b/typo3/sysext/workspaces/Classes/Controller/PreviewController.php
index 2b36111850d6b92247c58d9b58cb8dfee35a45ce..41345ab319a4ea8827fa0b0c28d2555aba658ac6 100644
--- a/typo3/sysext/workspaces/Classes/Controller/PreviewController.php
+++ b/typo3/sysext/workspaces/Classes/Controller/PreviewController.php
@@ -226,7 +226,6 @@ class PreviewController extends AbstractController
             'pageModule' => $pageModule,
             'inWorkspace' => $backendUser->workspace !== 0,
             'showRefreshLoginPopup' => isset($GLOBALS['TYPO3_CONF_VARS']['BE']['showRefreshLoginPopup']) ? (int)$GLOBALS['TYPO3_CONF_VARS']['BE']['showRefreshLoginPopup'] : false,
-            'debugInWindow' => $backendUser->uc['debugInWindow'] ? 1 : 0,
             'ContextHelpWindows' => [
                 'width' => 600,
                 'height' => 400