2048247 - FF 152.0.0 introduced a bug with fullscreen mode showing taskbar

Status: RESOLVED DUPLICATE of bug 2048501

(Core :: Widget: Win32, defect)

Description

[urbi]

Attachment: fullscreen_bug_ff152.png

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:152.0) Gecko/20100101 Firefox/152.0

Steps to reproduce:

FF 152.0.0 introduced the following new bug regarding fullscreen mode: If another YT video is already playing in picture-in-picture mode, and you click on fullscreen mode for a second YT video, Windows' taskbar icons are now on top of the (second) YT video, so there is no way to exit full screen mode anymore except hitting the Esc key. The bug is not there when entering fullscreen mode from within a (second) picture-in-picture window. It is 100 % reproducible here.

Actual results:

If another YT video is playing in picture-in-picture mode, and you click on fullscreen mode for a second YT video, Windows' Task List icons are now on top of the YT video, so there is no way to exit full screen mode anymore except hitting the Esc key. (see the attached screenshot).

Expected results:

Like it was until FF 151.0.x, any video playing in fullscreen mode should not show any overlayed taskbar icons.
Note that the bug is not there when entering fullscreen mode from within a (second) picture-in-picture window.

Comment 1

[urbi]

Another (maybe related) new bug in FF 152 is that the fullscreen mode of such a second YT video is sudenly exited when you set YouTube's time slider to a position whhich is not yet covered by the cache. Seems to me that something important is broken in terms of how FF handles fullscreen mode for videos.

Comment 2

[urbi]

Perhaps I should mention that I use the TranslucentTB app in my Windows 11 system (which makes the taskbar translucent). Don't know if this has an influenece somehow. But FF 152 should be able to correctly render fullscreen mode under any condition. The bug came in with today's update to FF 152.
BTW: I'm really tired of these kinds of bugs. Every new major version of FF breaks something. I mean, we all know that every piece of software has minor bugs from time to time. But with FF, they've been piling up lately. What exactly are you guys doing during the Nightly or Beta phase? Why doesn't something this serious get caught there? And almost every time, something is tinkered with on the newtabpage, so that the previous userContent.css no longer works (last time from FF 150 to 151). Instead of your (too?) frequent FF updates, rather make sure they're thoroughly tested before you release them! I don't think I'm the only one who has to put up with this.

Comment 3

[BugBot [:suhaib / :marco]]

The Bugbug bot thinks this bug should belong to the 'Core::Graphics' component, but is not confident enough to move the bug to that component.

Comment 4

[Ed Lee :Mardak]

The relevant code lives in widget/windows/ (especially nsWindowTaskbarConcealer.cpp, which handles ITaskbarList2::MarkFullscreenWindow and related "rudeness"/fullscreen marking logic for the OS taskbar).

Precedent from nearly identical bugs
These exact symptoms were triaged/fixed in Core :: Widget: Win32:

• Bug 1965699 ("Taskbar showing when a video is set to full screen") — Bugbug moved it to Widget: Win32; fixed there (involved widget.windows.fullscreen_marking_method and related changes). Many duplicates.
• Bug 1995838 ("Windows Taskbar is shown on top of PIP content in fullscreen") — originally in Toolkit :: Picture-in-Picture, moved to Widget: Win32 during fix. It has a duplicate (1995141) titled "Taskbar showing when entering fullscreen from picture-in-picture video (Windows 11)". Fixed by disabling Windows App SDK on PiP windows.
• Bug 1732517 (fullscreen window occluding taskbar) — moved to Widget: Win32.

Comment 5

[urbi]

Attachment: Perhaps your commit 805070c introduced the bug?

I noticed your commit 805070c. Can it be that this is the root cause for the mentioned issue? Can it be that your newly added if (!mPIPWindow) condition is not able to distinguish between whether the PiP window is for the video you want the Titlebar to be collapsed or for another video playing in a fullscreen window? If so, it would explain why the titlebar for the second video plaing in fullscreen mode is no longer hidden if one video is already playing in PiP mode.