Affected versions

• 89.0a1(20210418213620)

Affected platforms

• Windows 10x64

Steps to reproduce

1. Open Firefox and add the Library icon to the toolbar.
2. Open Library and Click on Bookmarks.
3. Click on the back arrow and repeat the step2.

Expected result

• Subpanels are opened as expected.

Actual result

• Bookmarks and History subpanels have a jumpy transition.

Regression range

• Last good revision: a5872317b9a09c03477c9bcc0b03d64f144e624b
  First bad revision: a55a815cbdc834561da11ae8736403774fd1ff8a
  Pushlog:
  https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=a5872317b9a09c03477c9bcc0b03d64f144e624b&tochange=a55a815cbdc834561da11ae8736403774fd1ff8a

Notes

• Attached a screen recording.

This issue can be seen with proton enabled and disabled as well. Attaching a video with proton disabled.

This looks like the animation itself is getting clipped.

I can reproduce this in both the bookmarks and history menus if they have a lot of entries. The lower part of the menu has a tendency to delay getting painted, so you see a clipped menu at the bottom briefly. Also occasionally the menu doesn't paint fully soon enough, so you see underlying content briefly where the popup would normally be.

This was visible on MacOS as well.

Bug 1692519 - Library menu is glitchy when opening or closing submenus

Profile in 89 early beta which has swiggle for popups enabled -
https://share.firefox.dev/3eGzDM4

Same but with basic layers for menus, which is what we'll ship with Proton -
https://share.firefox.dev/3gSl9v9

This isn't a bad experience. We don't experience a lot of jank. It could be smoother but we've been shipping with this this way for a long time.

Just a note, I reproduced this when doing my PM review. It's interesting because the AppMenu and Library Menu Panel both have the same animation, but I was only able to get the animation to lag / jump in the Library Menu Panel.

That said, I didn't consider this a required fix for 89. I suggest this get fixed for 90 though.

:atrif, is the problem addressed for you with latest nightly?

(In reply to Sotaro Ikeda [:sotaro] from comment #11)

:atrif, is the problem addressed for you with latest nightly?

Yes, I can no longer reproduce the issue with Firefox 90.0a1 (20210518213628) on Windows 10x64 and macOS 11.