2012291 - Right click context menu flashing on multi-monitor setup

Status: UNCONFIRMED

(Firefox :: Untriaged, defect)

Description

[Daniel Juranec]

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:147.0) Gecko/20100101 Firefox/147.0

Steps to reproduce:

My setup is: a 1440p 165Hz monitor and a 1080p 60Hz monitor, GTX 1080 Ti (576.88 driver), Windows 10 22H2. Recently, right click menus started "flashing" when appearing; menu appears for a split second, then disappears, then appears again. Can happen when right-clicking tabs (UI) or links (content). First invocation of the menu will usually flash, subsequent ones usually won't, until doing other actions like switching tabs, etc.

With mozregression narrowed it down to

2026-01-24T17:04:22.587000: DEBUG : Found commit message:
Bug 2002232 - Clean up top level widget painting. r=jwatt

Turns out this PaintSynchronously() call is needed, however we can do
better and centralize all the painting in a single PaintWindow():

 * DidPaintWindow is not needed, it's only used to dispatch an observer
   notification for testing.

 * WillPaintWindow and PaintWindow can be unified. Both can already run
   script in practice, and toplevel window bounds and widget bounds
   shouldn't change here anyways nowadays, since we recompute widget
   bounds only during the rendering loop.

Differential Revision: https://phabricator.services.mozilla.com/D273997

After more experimentation:

• Cannot replicate when only one monitor is enabled in Windows
• Cannot replicate when both monitors are set to 60Hz
• Flashing is most prominent and frequent when Firefox window is on the 60Hz display
• It was difficult to record with OBS - flashing usually wouldn't show on the recording

Attaching a screen recording where flashing is visible when seeking frame by frame (on a fresh FF profile), and a phone recording where flashing is more prominent (on my daily FF profile).

Actual results:

Right click menu flashes

Expected results:

Right click menu appears normally

Comment 1

[Daniel Juranec]

Attachment: screen recording of flashing

Comment 2

[Daniel Juranec]

Attachment: slow motion phone recording of flashing