Firefox custom tabs remain in recents screen after pressing back

[chenxiaolong]

Steps to reproduce

1. Click on a link in an app
2. In the URLCheck popup, open the link in Firefox
3. Press the system back button (or swipe gesture)

Expected behavior

The Firefox custom tab closes and is not present in Android's recents screen.

Actual behavior

The Firefox custom tab activity remains in the recents screen.

URLCheck version

3.4 (Github release)

Android version

Android 16

Android Custom/Specific ROM or Device

GrapheneOS

Other details

I can reproduce this with Firefox (141.0.3), Firefox Beta (142.0b9), and Firefox Nightly (143.0a1 - 2016107450). However, I do not see this issue with a Chromium-based browser (139.0.7258.62.1).

I wasn't sure if the issue was in URLCheck or Firefox because this issue does not happen when Firefox is set as the default browser.

When opening a custom tab with URLCheck + Firefox, I see this in the logcat:

2025-08-09 17:37:05.337354 -0400 I/ActivityTaskManager( 1207): START u0 {act=android.intent.action.VIEW dat=https://links.n.zavvi.com/... flg=0x10000000 xflg=0x4 cmp=org.mozilla.firefox_beta/org.mozilla.fenix.IntentReceiverActivity (has extras)} with LAUNCH_MULTIPLE from uid 10191 (sr=236176333) (BAL_ALLOW_VISIBLE_WINDOW) result code=0
2025-08-09 17:37:05.338544 -0400 V/WindowManagerShell( 2375): Transition requested (#357): android.os.BinderProxy@ace92ec TransitionRequestInfo { type = OPEN, triggerTask = TaskInfo{userId=0 taskId=1877 effectiveUid=10213 displayId=0 isRunning=true baseIntent=Intent { act=android.intent.action.VIEW dat=https://links.n.zavvi.com/... flg=0x10800000 cmp=org.mozilla.firefox_beta/org.mozilla.fenix.IntentReceiverActivity } baseActivity=ComponentInfo{org.mozilla.firefox_beta/org.mozilla.fenix.IntentReceiverActivity} topActivity=ComponentInfo{org.mozilla.firefox_beta/org.mozilla.fenix.IntentReceiverActivity} origActivity=null realActivity=ComponentInfo{org.mozilla.firefox_beta/org.mozilla.fenix.IntentReceiverActivity} numActivities=1 lastActiveTime=33448005 supportsMultiWindow=true resizeMode=1 isResizeable=true minWidth=-1 minHeight=-1 defaultMinSize=220 token=WCT{android.window.IWindowContainerToken$Stub$Proxy@940a6b5} topActivityType=1 pictureInPictureParams=null shouldDockBigOverlays=false launchIntoPipHostTaskId=-1 lastParentTaskIdBeforePip=-1 displayCutoutSafeInsets=Rect(0, 199 - 0, 0) topActivityInfo=ActivityInfo{850514a org.mozilla.fenix.IntentReceiverActivity} launchCookies=[] positionInParent=Point(0, 0) parentTaskId=-1 isFocused=false isVisible=false isVisibleRequested=false isTopActivityNoDisplay=false isSleeping=false locusId=null displayAreaFeatureId=1 isTopActivityTransparent=true isActivityStackTransparent=true lastNonFullscreenBounds=Rect(342, 893 - 1003, 2237) capturedLink=https://links.n.zavvi.com/<redacted> capturedLinkTimestamp=0 requestedVisibleTypes=-9 topActivityRequestOpenInBrowserEducationTimestamp=0 appCompatTaskInfo=AppCompatTaskInfo { topActivityInSizeCompat=false eligibleForLetterboxEducation= false isLetterboxEducationEnabled= false isLetterboxDoubleTapEnabled= false eligibleForUserAspectRatioButton= false topActivityBoundsLetterboxed= false isFromLetterboxDoubleTap= false topActivityLetterboxVerticalPosition= -1 topActivityLetterboxHorizontalPosition= -1 topActivityLetterboxWidth=-1 topActivityLetterboxHeight=-1 topActivityAppBounds=Rect(0, 0 - 1344, 2992) isUserFullscreenOverrideEnabled=false isSystemFullscreenOverrideEnabled=false hasMinAspectRatioOverride=false topActivityLetterboxBounds=null cameraCompatTaskInfo=CameraCompatTaskInfo { freeformCameraCompatMode=inactive}} topActivityMainWindowFrame=null}, pipChange = null, remoteTransition = null, displayChange = null, flags = 0, debugId = 357 }
2025-08-09 17:37:05.344778 -0400 I/AppWidgetServiceImpl( 1207): Received broadcast: android.intent.action.PACKAGE_UNSTOPPED on user 0
2025-08-09 17:37:05.368154 -0400 I/ActivityManager( 1207): Start proc 20485:org.mozilla.firefox_beta/u0a213 for next-top-activity {org.mozilla.firefox_beta/org.mozilla.fenix.IntentReceiverActivity}
2025-08-09 17:37:05.618929 -0400 I/AconfigPackage(20485): com.android.intentresolver is mapped to system
2025-08-09 17:37:05.818756 -0400 I/ActivityTaskManager( 1207): START u0 {act=android.intent.action.VIEW dat=https://links.n.zavvi.com/... xflg=0x4 cmp=org.mozilla.firefox_beta/org.mozilla.fenix.customtabs.ExternalAppBrowserActivity (has extras)} with LAUNCH_MULTIPLE from uid 10213 (sr=5266383) (BAL_ALLOW_VISIBLE_WINDOW) result code=0
2025-08-09 17:37:05.919473 -0400 I/BroadcastQueue( 1207): BOOT_COMPLETED_BROADCAST_COMPLETION_LATENCY_REPORTED action:android.intent.action.BOOT_COMPLETED dispatchLatency:0 completeLatency:295 dispatchRealLatency:1 completeRealLatency:295 receiversSize:1 userId:0 userType:android.os.usertype.full.SYSTEM
2025-08-09 17:37:06.051113 -0400 W/ActivityManager( 1207): Receiver with filter android.content.IntentFilter@8ac302d already registered for pid 20485, callerPackage is org.mozilla.firefox_beta
2025-08-09 17:37:06.079659 -0400 V/WindowManager( 1207): Sent Transition (#357) createdAt=08-09 17:37:05.329 via request=TransitionRequestInfo { type = OPEN, triggerTask = TaskInfo{userId=0 taskId=1877 effectiveUid=10213 displayId=0 isRunning=true baseIntent=Intent { act=android.intent.action.VIEW dat=https://links.n.zavvi.com/... flg=0x10800000 cmp=org.mozilla.firefox_beta/org.mozilla.fenix.IntentReceiverActivity } baseActivity=ComponentInfo{org.mozilla.firefox_beta/org.mozilla.fenix.IntentReceiverActivity} topActivity=ComponentInfo{org.mozilla.firefox_beta/org.mozilla.fenix.IntentReceiverActivity} origActivity=null realActivity=ComponentInfo{org.mozilla.firefox_beta/org.mozilla.fenix.IntentReceiverActivity} numActivities=1 lastActiveTime=33448005 supportsMultiWindow=true resizeMode=1 isResizeable=true minWidth=-1 minHeight=-1 defaultMinSize=220 token=WCT{RemoteToken{5f9eadc Task{f4a595c #1877 type=standard I=org.mozilla.firefox_beta/org.mozilla.fenix.customtabs.ExternalAppBrowserActivity}}} topActivityType=1 pictureInPictureParams=null shouldDockBigOverlays=false launchIntoPipHostTaskId=-1 lastParentTaskIdBeforePip=-1 displayCutoutSafeInsets=Rect(0, 199 - 0, 0) topActivityInfo=ActivityInfo{32037e5 org.mozilla.fenix.IntentReceiverActivity} launchCookies=[] positionInParent=Point(0, 0) parentTaskId=-1 isFocused=false isVisible=false isVisibleRequested=false isTopActivityNoDisplay=false isSleeping=false locusId=null displayAreaFeatureId=1 isTopActivityTransparent=true isActivityStackTransparent=true lastNonFullscreenBounds=Rect(342, 893 - 1003, 2237) capturedLink=https://links.n.zavvi.com/<redacted> capturedLinkTimestamp=0 requestedVisibleTypes=-9 topActivityRequestOpenInBrowserEducationTimestamp=0 appCompatTaskInfo=AppCompatTaskInfo { topActivityInSizeCompat=false eligibleForLetterboxEducation= false isLetterboxEducationEnabled= false isLetterboxDoubleTapEnabled= false eligibleForUserAspectRatioButton= false topActivityBoundsLetterboxed= false isFromLetterboxDoubleTap= false topActivityLetterboxVerticalPosition= -1 topActivityLetterboxHorizontalPosition= -1 topActivityLetterboxWidth=-1 topActivityLetterboxHeight=-1 topActivityAppBounds=Rect(0, 0 - 1344, 2992) isUserFullscreenOverrideEnabled=false isSystemFullscreenOverrideEnabled=false hasMinAspectRatioOverride=false topActivityLetterboxBounds=null cameraCompatTaskInfo=CameraCompatTaskInfo { freeformCameraCompatMode=inactive}} topActivityMainWindowFrame=null}, pipChange = null, remoteTransition = null, displayChange = null, flags = 0, debugId = 357 }

When closing a custom tab with URLCheck + Firefox:

2025-08-09 17:33:02.904889 -0400 V/WindowManagerShell( 2375): Transition requested (#319): android.os.BinderProxy@c36af79 TransitionRequestInfo { type = CLOSE, triggerTask = TaskInfo{userId=0 taskId=1869 effectiveUid=10213 displayId=0 isRunning=false baseIntent=Intent { act=android.intent.action.VIEW dat=https://links.n.zavvi.com/... cmp=org.mozilla.firefox_beta/org.mozilla.fenix.customtabs.ExternalAppBrowserActivity } baseActivity=null topActivity=null origActivity=null realActivity=ComponentInfo{org.mozilla.firefox_beta/org.mozilla.fenix.customtabs.ExternalAppBrowserActivity} numActivities=0 lastActiveTime=33168742 supportsMultiWindow=true resizeMode=2 isResizeable=true minWidth=-1 minHeight=-1 defaultMinSize=220 token=WCT{android.window.IWindowContainerToken$Stub$Proxy@d55c4be} topActivityType=1 pictureInPictureParams=null shouldDockBigOverlays=false launchIntoPipHostTaskId=-1 lastParentTaskIdBeforePip=-1 displayCutoutSafeInsets=Rect(0, 0 - 0, 0) topActivityInfo=null launchCookies=[] positionInParent=Point(0, 0) parentTaskId=-1 isFocused=true isVisible=true isVisibleRequested=true isTopActivityNoDisplay=false isSleeping=false locusId=null displayAreaFeatureId=1 isTopActivityTransparent=false isActivityStackTransparent=true lastNonFullscreenBounds=Rect(342, 893 - 1003, 2237) capturedLink=https://links.n.zavvi.com/<redacted> capturedLinkTimestamp=21183746 requestedVisibleTypes=-9 topActivityRequestOpenInBrowserEducationTimestamp=0 appCompatTaskInfo=AppCompatTaskInfo { topActivityInSizeCompat=false eligibleForLetterboxEducation= false isLetterboxEducationEnabled= false isLetterboxDoubleTapEnabled= false eligibleForUserAspectRatioButton= false topActivityBoundsLetterboxed= false isFromLetterboxDoubleTap= false topActivityLetterboxVerticalPosition= -1 topActivityLetterboxHorizontalPosition= -1 topActivityLetterboxWidth=-1 topActivityLetterboxHeight=-1 topActivityAppBounds=Rect(0, 0 - 0, 0) isUserFullscreenOverrideEnabled=false isSystemFullscreenOverrideEnabled=false hasMinAspectRatioOverride=false topActivityLetterboxBounds=null cameraCompatTaskInfo=CameraCompatTaskInfo { freeformCameraCompatMode=undefined}} topActivityMainWindowFrame=null}, pipChange = null, remoteTransition = null, displayChange = null, flags = 0, debugId = 319 }
2025-08-09 17:33:02.985640 -0400 V/WindowManager( 1207): Sent Transition (#319) createdAt=08-09 17:33:02.903 via request=TransitionRequestInfo { type = CLOSE, triggerTask = TaskInfo{userId=0 taskId=1869 effectiveUid=10213 displayId=0 isRunning=false baseIntent=Intent { act=android.intent.action.VIEW dat=https://links.n.zavvi.com/... cmp=org.mozilla.firefox_beta/org.mozilla.fenix.customtabs.ExternalAppBrowserActivity } baseActivity=null topActivity=null origActivity=null realActivity=ComponentInfo{org.mozilla.firefox_beta/org.mozilla.fenix.customtabs.ExternalAppBrowserActivity} numActivities=0 lastActiveTime=33168742 supportsMultiWindow=true resizeMode=2 isResizeable=true minWidth=-1 minHeight=-1 defaultMinSize=220 token=WCT{RemoteToken{17c5e85 Task{4110841 #1869 type=standard I=org.mozilla.firefox_beta/org.mozilla.fenix.customtabs.ExternalAppBrowserActivity}}} topActivityType=1 pictureInPictureParams=null shouldDockBigOverlays=false launchIntoPipHostTaskId=-1 lastParentTaskIdBeforePip=-1 displayCutoutSafeInsets=Rect(0, 0 - 0, 0) topActivityInfo=null launchCookies=[] positionInParent=Point(0, 0) parentTaskId=-1 isFocused=true isVisible=true isVisibleRequested=true isTopActivityNoDisplay=false isSleeping=false locusId=null displayAreaFeatureId=1 isTopActivityTransparent=false isActivityStackTransparent=true lastNonFullscreenBounds=Rect(342, 893 - 1003, 2237) capturedLink=https://links.n.zavvi.com/<redacted> capturedLinkTimestamp=21183746 requestedVisibleTypes=-9 topActivityRequestOpenInBrowserEducationTimestamp=0 appCompatTaskInfo=AppCompatTaskInfo { topActivityInSizeCompat=false eligibleForLetterboxEducation= false isLetterboxEducationEnabled= false isLetterboxDoubleTapEnabled= false eligibleForUserAspectRatioButton= false topActivityBoundsLetterboxed= false isFromLetterboxDoubleTap= false topActivityLetterboxVerticalPosition= -1 topActivityLetterboxHorizontalPosition= -1 topActivityLetterboxWidth=-1 topActivityLetterboxHeight=-1 topActivityAppBounds=Rect(0, 0 - 0, 0) isUserFullscreenOverrideEnabled=false isSystemFullscreenOverrideEnabled=false hasMinAspectRatioOverride=false topActivityLetterboxBounds=null cameraCompatTaskInfo=CameraCompatTaskInfo { freeformCameraCompatMode=undefined}} topActivityMainWindowFrame=null}, pipChange = null, remoteTransition = null, displayChange = null, flags = 0, debugId = 319 }

When opening a custom tab with Firefox only:

2025-08-09 17:33:35.799349 -0400 I/ActivityTaskManager( 1207): START u0 {act=android.intent.action.VIEW dat=https://links.n.zavvi.com/... xflg=0x4 cmp=org.mozilla.firefox_beta/org.mozilla.fenix.IntentReceiverActivity (has extras)} with LAUNCH_MULTIPLE from uid 10209 (sr=125543098) (BAL_ALLOW_VISIBLE_WINDOW) result code=0
2025-08-09 17:33:35.800125 -0400 V/WindowManagerShell( 2375): Transition requested (#327): android.os.BinderProxy@510b2f0 TransitionRequestInfo { type = OPEN, triggerTask = TaskInfo{userId=0 taskId=1838 effectiveUid=10209 displayId=0 isRunning=true baseIntent=Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10200000 pkg=com.fastmail.app cmp=com.fastmail.app/.ui.webview.WebViewActivity } baseActivity=ComponentInfo{com.fastmail.app/com.fastmail.app.ui.webview.WebViewActivity} topActivity=ComponentInfo{org.mozilla.firefox_beta/org.mozilla.fenix.IntentReceiverActivity} origActivity=null realActivity=ComponentInfo{com.fastmail.app/com.fastmail.app.ui.webview.WebViewActivity} numActivities=2 lastActiveTime=33238465 supportsMultiWindow=true resizeMode=1 isResizeable=true minWidth=-1 minHeight=-1 defaultMinSize=220 token=WCT{android.window.IWindowContainerToken$Stub$Proxy@4418069} topActivityType=1 pictureInPictureParams=null shouldDockBigOverlays=false launchIntoPipHostTaskId=-1 lastParentTaskIdBeforePip=-1 displayCutoutSafeInsets=Rect(0, 0 - 0, 0) topActivityInfo=ActivityInfo{f39daee org.mozilla.fenix.IntentReceiverActivity} launchCookies=[android.os.BinderProxy@493a950] positionInParent=Point(0, 0) parentTaskId=-1 isFocused=true isVisible=true isVisibleRequested=true isTopActivityNoDisplay=false isSleeping=false locusId=null displayAreaFeatureId=1 isTopActivityTransparent=true isActivityStackTransparent=false lastNonFullscreenBounds=Rect(342, 893 - 1003, 2237) capturedLink=https://links.n.zavvi.com/<redacted> capturedLinkTimestamp=0 requestedVisibleTypes=-9 topActivityRequestOpenInBrowserEducationTimestamp=0 appCompatTaskInfo=AppCompatTaskInfo { topActivityInSizeCompat=false eligibleForLetterboxEducation= false isLetterboxEducationEnabled= false isLetterboxDoubleTapEnabled= false eligibleForUserAspectRatioButton= false topActivityBoundsLetterboxed= false isFromLetterboxDoubleTap= false topActivityLetterboxVerticalPosition= -1 topActivityLetterboxHorizontalPosition= -1 topActivityLetterboxWidth=-1 topActivityLetterboxHeight=-1 topActivityAppBounds=Rect(0, 0 - 1344, 2992) isUserFullscreenOverrideEnabled=false isSystemFullscreenOverrideEnabled=false hasMinAspectRatioOverride=false topActivityLetterboxBounds=null cameraCompatTaskInfo=CameraCompatTaskInfo { freeformCameraCompatMode=inactive}} topActivityMainWindowFrame=null}, pipChange = null, remoteTransition = null, displayChange = null, flags = 0, debugId = 327 }
2025-08-09 17:33:35.825005 -0400 I/ActivityManager( 1207): Start proc 17215:org.mozilla.firefox_beta/u0a213 for next-top-activity {org.mozilla.firefox_beta/org.mozilla.fenix.IntentReceiverActivity}
2025-08-09 17:33:36.033693 -0400 I/AconfigPackage(17215): com.android.intentresolver is mapped to system
2025-08-09 17:33:36.233249 -0400 I/ActivityTaskManager( 1207): START u0 {act=android.intent.action.VIEW dat=https://links.n.zavvi.com/... xflg=0x4 cmp=org.mozilla.firefox_beta/org.mozilla.fenix.customtabs.ExternalAppBrowserActivity (has extras)} with LAUNCH_MULTIPLE from uid 10213 (sr=55326779) (BAL_ALLOW_VISIBLE_WINDOW) result code=0
2025-08-09 17:33:36.424241 -0400 W/ActivityManager( 1207): Receiver with filter android.content.IntentFilter@13aeeb7 already registered for pid 17215, callerPackage is org.mozilla.firefox_beta
2025-08-09 17:33:36.431900 -0400 V/WindowManager( 1207): Sent Transition (#327) createdAt=08-09 17:33:35.792 via request=TransitionRequestInfo { type = OPEN, triggerTask = TaskInfo{userId=0 taskId=1838 effectiveUid=10209 displayId=0 isRunning=true baseIntent=Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10200000 pkg=com.fastmail.app cmp=com.fastmail.app/.ui.webview.WebViewActivity } baseActivity=ComponentInfo{com.fastmail.app/com.fastmail.app.ui.webview.WebViewActivity} topActivity=ComponentInfo{org.mozilla.firefox_beta/org.mozilla.fenix.IntentReceiverActivity} origActivity=null realActivity=ComponentInfo{com.fastmail.app/com.fastmail.app.ui.webview.WebViewActivity} numActivities=2 lastActiveTime=33238465 supportsMultiWindow=true resizeMode=1 isResizeable=true minWidth=-1 minHeight=-1 defaultMinSize=220 token=WCT{RemoteToken{1ee3f5b Task{115256b #1838 type=standard I=com.fastmail.app/.ui.webview.WebViewActivity}}} topActivityType=1 pictureInPictureParams=null shouldDockBigOverlays=false launchIntoPipHostTaskId=-1 lastParentTaskIdBeforePip=-1 displayCutoutSafeInsets=Rect(0, 0 - 0, 0) topActivityInfo=ActivityInfo{5d57d89 org.mozilla.fenix.IntentReceiverActivity} launchCookies=[android.os.BinderProxy@c011284] positionInParent=Point(0, 0) parentTaskId=-1 isFocused=true isVisible=true isVisibleRequested=true isTopActivityNoDisplay=false isSleeping=false locusId=null displayAreaFeatureId=1 isTopActivityTransparent=true isActivityStackTransparent=false lastNonFullscreenBounds=Rect(342, 893 - 1003, 2237) capturedLink=https://links.n.zavvi.com/<redacted> capturedLinkTimestamp=0 requestedVisibleTypes=-9 topActivityRequestOpenInBrowserEducationTimestamp=0 appCompatTaskInfo=AppCompatTaskInfo { topActivityInSizeCompat=false eligibleForLetterboxEducation= false isLetterboxEducationEnabled= false isLetterboxDoubleTapEnabled= false eligibleForUserAspectRatioButton= false topActivityBoundsLetterboxed= false isFromLetterboxDoubleTap= false topActivityLetterboxVerticalPosition= -1 topActivityLetterboxHorizontalPosition= -1 topActivityLetterboxWidth=-1 topActivityLetterboxHeight=-1 topActivityAppBounds=Rect(0, 0 - 1344, 2992) isUserFullscreenOverrideEnabled=false isSystemFullscreenOverrideEnabled=false hasMinAspectRatioOverride=false topActivityLetterboxBounds=null cameraCompatTaskInfo=CameraCompatTaskInfo { freeformCameraCompatMode=inactive}} topActivityMainWindowFrame=null}, pipChange = null, remoteTransition = null, displayChange = null, flags = 0, debugId = 327 }

When closing a custom tab with Firefox only:

2025-08-09 17:41:37.577919 -0400 V/WindowManagerShell( 2375): Transition requested (#369): android.os.BinderProxy@a9c2bcd TransitionRequestInfo { type = CLOSE, triggerTask = null, pipChange = null, remoteTransition = null, displayChange = null, flags = 0, debugId = 369 }
2025-08-09 17:41:37.629007 -0400 V/WindowManager( 1207): Sent Transition (#369) createdAt=08-09 17:41:37.576 via request=TransitionRequestInfo { type = CLOSE, triggerTask = null, pipChange = null, remoteTransition = null, displayChange = null, flags = 0, debugId = 369 }

Acknowledgements

• I have searched the existing issues and this is a new ticket, NOT a duplicate or related to another open issue.
• I have written a short but informative title.
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[TrianguloY]

Thanks for the report and the detailed logcat!
I think I know what the issue is, and there is no 'good' solution, the only thing I can think of is to add a toggle to specify the behavior on this specific situation...or add capabilities to the flags editor module to get/set flags (which I should add anyway).

If I'm not mistaken, the issue is with the FLAG_ACTIVITY_EXCLUDE_FROM_RECENTS. The app tries to keep all flags that are sent to itself (and try to maintain the original as much as possible) however the app itself must not be kept on recents. So the app requests to not be present on the recents screen, but that makes android launch the intent with that flag, and in the past this made all links opened with URLCheck not be kept on recents. I fixed that by just removing the flag, but that means that when the original intent has it, it is still removed.
I'm not sure if there is a better solution, other than detect if it's a custom tab and set the flag. I personally prefer the current behaviour, but I can see why others may not.
I'll consider adding a toggle for this, and adding the automations to the flags module (where you can test this btw).

[chenxiaolong]

Thanks for digging into this!

I tried all 4 combinations of true/false here:

URLCheck/app/src/main/java/com/trianguloy/urlchecker/modules/companions/Flags.java

Lines 21 to 24 in c5b9ce4

	public static final Map<String, Boolean> DEFAULT_STATE = Map.of(
	"ACTIVITY_NEW_TASK", true,
	"ACTIVITY_EXCLUDE_FROM_RECENTS", false
	);

and also tried removing the default flags completely. I don't see any change in behavior though. The Firefox custom tabs seem to always remain in recents after pressing back.

However, while I trying to see why this only happened with Firefox and not Chromium, I saw this:

https://github.com/mozilla-firefox/firefox/blob/e93030b39fb3f3e8f9279bbb57107a8315d2c40a/mobile/android/fenix/app/src/main/AndroidManifest.xml#L532-L541

vs. Chromium's:

https://source.chromium.org/chromium/chromium/src/+/main:chrome/android/java/AndroidManifest.xml;l=504-512;drc=789fc8c81590392932bceb85a43b15e04ee29c8d

Firefox sets autoRemoveFromRecents=false, but only calls Activity.finishAndRemoveTask() when pressing the close button the toolbar. Indeed, if I press the close button in a custom tab with URLCheck + Firefox, the custom tab no longer exists in recents. If I press back, then it stays in recents.

Seeing this, I have no idea why the back button successfully removes Firefox from recents when it's the default browser. Perhaps an Android bug?

---

While reading about autoRemoveFromRecents, I found that its default value depends on whether ACTIVITY_NEW_DOCUMENT is present. Even though Firefox is explicitly setting autoRemoveFromRecents=false, if I configure URLCheck to set ACTIVITY_NEW_DOCUMENT, then this issue no longer occurs. I have no idea why.

It's an ugly hack, but seems to behave as expected with both Firefox and Chromium. I'm not seeing any weird issues when opening a single custom tab, multiple custom tabs, or the main browser activity (no custom tabs). This workaround is good enough for me (thanks for the flags module!).

[soshial]

I also have the same issue and it's a bit annoying. Thanks into digging into it! Is the solution somewhere near?

[TrianguloY]

I'm afraid not. Sorry