Alt-text and buger-/add-ons- menus not displaying in Firefox and Thunderbird


since last big update of TW on my laptop, I have troubles with both Firefox and Thunderbird not displaying some overlays.

In Firefox, it happens both with the “alt-text” of pictures, and with drop down menu of add-ons (e.g.: the block-list of NoScript) and of the “≡” button (aka “buger menu”).
(right-click contextual menus and the legacy menu bar still display correctly).

In Thunderbird, I’ve noticed it only with the “≡” button’s menu.

I haven’t noticed it elsewhere, so I suppose it’s specifically happening with the Gecko engine these two software are based on.

The symptom is that a rectangle gets allocated where the alt-text or menu should go, but nothing is rendered in this rectangle, the content stay frozen with whatever was underneath when it should have displayed (even if the page has been made scroll, it still shows the old content. That’s how I noticed the rectangle was indeed created, just not filled).

As it looked as some accelerated rendering trouble, I tried disabling hardware acceleration in Firefox’ preferences, but it didn’t change much.

No error message are displayed in the terminal. Nothing shows up in systemd’s journal neither.

At this point I have no idea where to investigate next.

My desktop environment is Plasma running in X11, the GPU is an ancient NVIDIA GT218M NVS 3100M running on Mesa’s nouveau driver.

That’s how it looks like:

Okay further investigations:
I have another laptop, that is running a different distro (Manjaro ARM) but also Firefox 87, and doesn’t exhibit these artifacts.

When remotely (ssh -X) running Firefox from Manjaro ARM but displaying it on the Tumbleweed laptop, it suddenly display these artifacts.
When remotely running Firefox from Tumbleweed on the Manjaro ARM laptop, it suddenly displays the same artifacts.

So it’s probably not due to Firefox itself, it’s probably some composition bugs.

Possible sources:

  • driver problems? Tumbleweed has mesa 20.3.5 running nouveau on Nvidia hardware (whears the Manjaro ARM laptop has mesa 21.0.1 running panfrost on Mali T860 hardware)
  • compositor problem? Tumbleweed has kwin_x11 version 5.21.4 running in OpenGL3 composition (whereas the Manjaro ARM laptop has kwin_x11 5.21.4, also GL3)

Found the difference:

  • compositor was disabled for some reason on Tumbleweed.

So the key problem is:

when compositor is disables some overlays don’t show properly in Firefox.