Firefox CSD: Mouse click offset and titlebar gap at 200% HiDPI scaling

[rodolfomartinez]

Distribution

Debian 13 Cinnamon / Maple Linux Core v1

Package version

6.4.10

Graphics hardware in use

Intel Corporation Comet Lake UHD Graphics (rev 04)

Frequency

Always

Bug description

Cinnamon version: Cinnamon 6.4.10
Muffin version: mutter 6.4.1
Distribution: Debian 13 Trixie / Maple Linux Core
Display: 4K display with 200% UI scaling (preset, not fractional)
Graphics driver: 00:02.0 VGA compatible controller: Intel Corporation Comet Lake UHD Graphics (rev 04)

Issue:
With 200% HiDPI scaling enabled, Firefox (and possibly other CSD apps)
develops a ~50px gap above the title bar after minimize/maximize operations.
The mouse clickable area doesn't match the visual window position - you must
click slightly above UI elements to interact with them.

Steps to reproduce

Reproduction:

1. Set UI scaling to 200% in Cinnamon settings
2. Open Firefox
3. Minimize and restore the window, or move between workspaces
4. Observe gap above window and offset click targets

Expected behavior

There should be no gap or mouse cursor offset.

Additional information

Workaround:
Launching Firefox with MOZ_GTK_TITLEBAR_DECORATION=system may resolve the issue (seems to work so far)

[mtwebster]

Screenshot? I can't reproduce this.

edit: And what firefox version?

[leigh123linux]

I believe this is a firefox and thunderbird regression as it only recently started happening after they were updated.

[rodolfomartinez]

This happens in 140.5.0 esr. It didn't happen for awhile but then happened when I came out of standby.
If you look at the second screenshot, my mouse cursor is offset. I have to click above where things should be.

[rodolfomartinez]

If I maximize it happens works again. For reference I am using Maple Linux, which is from a lightly modified Debian 13 cinnamon live ISO