Open Bug 1746660 Opened 8 months ago Updated 8 months ago

Incorrect scrollbar mode on startup when using "Automatically based on mouse or trackpad" setting in macOS


(Thunderbird :: Mail Window Front End, defect)

Thunderbird 91


(Not tracked)



(Reporter: mozbugzilla2021, Unassigned)


(Blocks 1 open bug)


User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:95.0) Gecko/20100101 Firefox/95.0

Steps to reproduce:

  1. Set “Show scroll bars” to “Automatically based on mouse or trackpad” in macOS System Preferences General pane
  2. Plug in external mouse
  3. Launch Thunderbird

Actual results:

Overlay scrollbars are used, as if the OS is in trackpad mode, when it is not. The horizontal scrollbar for message bodies is broken and will not respond to mouse button input.

Expected results:

Scrollbars should be displayed normally.

If the mouse is unplugged and replugged while Thunderbird is running, it will start showing the scrollbars in the correct mode, so this is only a problem with the way it detects the scrollbar mode on startup.

This is a regression from the previous LTS version of Thunderbird.

Blocks: tb91found
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