Affected versions

• 90.0a1 (20210510160229)
• 89.0b10 (20210506185706)

Affected platforms

• macOS 11.3.1
• macOS 10.15

Preconditions

• Have Automatically hide and show the menu bar activated

Steps to reproduce

1. Open Firefox double click to stretch it to the available screen.
2. Enter Full Screen by pressing the green button.
3. Press the Fullscreen green button again.

Expected result

• Firefox exits full screen with no visual glitches.

Actual result

• A blank bar can be seen on top of the browser while Firefox exits fullscreen.

Regression range

• Last good revision: 239c833a3b6a9e90b1b482c1d619e7afdc74deef
  First bad revision: 0b9387e9e623ee132559a858a8d7782f6c4af213
  Pushlog:
  https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=239c833a3b6a9e90b1b482c1d619e7afdc74deef&tochange=0b9387e9e623ee132559a858a8d7782f6c4af213
• Possible regressor: bug 738335.

Notes

• Attached a screen recording.
• This is reproducible with native fullscreen disabled and enabled as well.

I am using FF 88 on Macos Big Sur and have the same experience.

Another thing that is happening is that the tabs cannot be clicked until moving the mouse a bit more down (after the come down when reaching the top of the screen in fullscreen mode).
If you try to work fast (and be more efficient) it'll be hard since moving down too much will cause the tab bar to go up again.
So need to be very precise which mean slow (as well)

I wish I could just have the option to use tabs on the bottom of the screen instead of the top.
(I don't mean below the menu bar like it use to be before FF4, I mean bottom of the screen where the status bar used to be)

Please make Firefox a productive browser again :)

Harry, could you look at this one please? Thanks

I'm going to downgrade this to a P3. It requires setting a non-default system preference that's fairly difficult to find and putting a window that's already maximized in fullscreen mode. That's quite an edge case IMO. Also, the result is a low-severity visual glitch.

(In reply to izak723 from comment #1)

Another thing that is happening is that the tabs cannot be clicked until moving the mouse a bit more down (after the come down when reaching the top of the screen in fullscreen mode).

I'm assuming you mean this is an issue when the window is maximized but not in fullscreen mode? If so, I don't think that's a new issue. Other apps have the same issue: you can't access the uppermost part of the window when the unhidden menu bar descends. I don't think there's really anything we can do to fix it. As a workaround, you could enable the title bar in Firefox (you can do so from the bottom left corner of the customize window). That way, the unhidden menu bar would just cover the title bar.