User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:108.0) Gecko/20100101 Firefox/108.0

Steps to reproduce:

1. Enter fullscreen, (F11)
2. Minimize browser window or open different app,
3. Open browser window from the taskbar.

Actual results:

White bars appear around the window (see exp1.png)

Expected results:

No white bars around the window

Steps to reproduce:

1. Disable native titlebar if any (default)
2. Enter fullscreen, (F11)
3. Minimize the Nightly window
4. Click the Nightly task button in taskbar

Regression window:
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=98e7f7bfffc4f9f164b985d51a11feaeec37dd7f&tochange=ae18bb00fae2a2d15ed7817e4178fddf2ddecbb3

:emilio, since you are the author of the regressor, bug 1797463, could you take a look? Also, could you set the severity field?

For more information, please visit auto_nag documentation.

FYI, Firefox 107 RC is not affected by the uplift patch in bug 1797463.

When minimizing a fullscreen window, frame state is kept with
mFullscreenMode = true but mSizeMode = nsSizeMode_Minimized.

Calling EnsureSizeMode(nsSizeMode_Fullscreen) in this state would call
EnsureFullscreenMode(true), but that'd bail out without actually
setting the fullscreen sizemode, causing confusion.

Before the regressing patch that was papered over because
nsSizeMode_Fullscreen was passed explicitly to OnSizeModeChange(), but
the underlying state was already wrong before my patch.

Add some comments and documentation to the fullscreen-relevant members,
since initially I was rather confused about this code.

https://hg.mozilla.org/mozilla-central/rev/7ae4a0fd85bf

Comment on attachment 9303258 [details]
Bug 1800416 - Ensure setting fullscreen actually ends up with a fullscreen sizemode. r=cmartin,mhowell

Beta/Release Uplift Approval Request

• User impact if declined: comment 0
• Is this code covered by automated tests?: No
• Has the fix been verified in Nightly?: Yes
• Needs manual test from QE?: Yes
• If yes, steps to reproduce: comment 0
• List of other uplifts needed: none
• Risk to taking this patch: Low
• Why is the change risky/not risky? (and alternatives if risky): Very well-targeted patch.
• String changes made/needed: none
• Is Android affected?: No

Comment on attachment 9303258 [details]
Bug 1800416 - Ensure setting fullscreen actually ends up with a fullscreen sizemode. r=cmartin,mhowell

Approved for 108.0b2

https://hg.mozilla.org/releases/mozilla-beta/rev/4f12b8b25400

Reproduced the issue with Firefox 108.0a1 on Windows 10x64 by following the STR from comment 0 and comment 1.
The issue is verified fixed with Firefox 109.0a1 (20221114214403) and Firefox 108.0b1 (20221115015959) treeherder build from comment 9 on Windows 10x64, Windows 11x64 and Windows 7x64. The white bars are no longer displayed after following the steps from comment 1.