Affected versions

• 88.0a1 (20210317212527)
• 87.0 (20210315170302)
• 86.0.1 (20210310152336)

Affected platforms

• macOS 11.2.2

Steps to reproduce

1. Open Firefox and install a random addon.
2. Enter and exit Fullscreen mode.

Expected result

• Dropdown addon menu is displayed as expected.

Actual result

• Dropdown menu addon has another arrow.

Regression range

• I will search for one ASAP if there is one.

Notes

• Attached a screen recording.

What happens here is that the arrow position shifts and the old shadow sticks around. The shadow shape is only computed when the panel is initially shown, or if it is resized.
If this is not a recent regression, I would not treat it as overly important, because the Proton theme eliminates the arrow.

(In reply to Markus Stange [:mstange] from comment #1)

What happens here is that the arrow position shifts and the old shadow sticks around. The shadow is only computed when the panel is initially shown, or if it is resized.
If this is not a recent regression, I would not treat it as overly important, because the Proton theme eliminates the arrow.

Not a recent regression from what I see. Reproduced with 71.0a1 (20190902213933) as well (it seems that on older builds I cannot open fullscreen on my macOS M1).

This is the pushlog made on macOS 10.12:
https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=b3158d143d833ec52c938e5235c1f86409fb764b&tochange=df860e79a6a3cc41712cfd86ffbd18cf84fce626

Possible regressor: bug 1491438.

As mentioned in comment 1, as of Proton, this is no longer an issue.