Graphical glitches with Firefox when using fractional scaling and KDE-Rounded-Corners

[rmariotti]

I'm experiencing graphical issues when using the KDE-Rounded-Corners plugin alongside Firefox on Wayland with fractional scaling enabled.

When fractional scaling is active, all menus in Firefox leave artifacts when closing (mostly ghost-windows of part of the menus themselves). These issues go away when KDE-Rounded-Corners is disabled or the scale is reset to 100% or 200%.

How to reproduce

1. Ensure KDE-Rounded-Corners is enabled.
2. Set scaling to 125% or 150% (or other fractional scaling).
3. Launch Firefox.
4. Click multiple times on the ☰ icon in the top right corner of Firefox to open and close the menu multiple times.
5. Observe the in the top right corner glitching.

Environment

• OS: Debian Sid
• KDE Plasma version: 6.3.5
• Compositor: kwin_wayland
• Firefox version: 128.11.0esr, 139.0.4
• KDE-Rounded-Corners version: 0.7.2.6.3.5
• Graphics drivers: firmware-amd-graphics

This bug seems specific to the interaction between Firefox, KDE-Rounded-Corners and fractional scaling. I've tried multiple settings in Firefox and Plasma that could have been reasonably related to the problem, but the problem persists. Other applications (I've tested some other GTK apps) appear unaffected under the same conditions.

I really appreciate the effort you’ve put into this plugin and wanted to thank you for building and maintaining it.

[matinlotfali]

@rmariotti Thank you for the report. May I ask that you also send me a screen recording of the issue?

[rmariotti]

@matinlotfali I could not capture the glitch with Spectacle (I still attached the capture). I've recorded the glitch with my phone camera, the quality is super bad but should give you an idea of what is happening.

Spectacle screen capture: https://github.com/user-attachments/assets/4103b1a2-55c7-4a9d-9f40-9a06ac52e1a8

Phone screen capture: https://github.com/user-attachments/assets/15758953-b55c-4824-987c-68a8659039a8

[unixr77]

i can confirm this. When effect is active, Firefox menus start flashing.

[matinlotfali]

I also confirm that I see this issue. I think it is a KWin issue because I can also see this issue on the Invert effect.