I get the same errors about descriptor, but no mention of mlt or missing libraries.
I tried the flatpak version and that seems to be working.

There should be a config file in ~/.config/MangoHud (you can check more details in the GitHub page https://github.com/flightlessmango/MangoHud#hud-configuration).

By adding frametime=0 to the config file, you should be able to remove the frametime measurement from the FPS display.

Sorry for the late reply. I didn't get notified of new messages.

I found these bug reports on Bugzilla:

• https://bugzilla.mozilla.org/show_bug.cgi?id=1835322
• https://bugzilla.mozilla.org/show_bug.cgi?id=1843647
• https://bugzilla.mozilla.org/show_bug.cgi?id=1845249

At a quick glance these seem to be the same issue you noticed.

Based on some reports in Bugzilla, the missing option to open in app seems to be a few month old bug. A workaround that I've been using is to "Share" the link with the app you want. Assuming the app supports it in the first place.