User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:95.0) Gecko/20100101 Firefox/95.0
Steps to reproduce:
- Set “Show scroll bars” to “Automatically based on mouse or trackpad” in macOS System Preferences General pane
- Plug in external mouse
- Launch Thunderbird
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.
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.