As per https://blog.gtk.org/2024/01/28/new-renderers-for-gtk/ and https://www.phoronix.com/news/GTK-4.16-Released :

You can still use either a new OpenGL renderer or the old OpenGL renderer. This can be set with the GSK_RENDERER environment variable (e.g. GSK_RENDERER=gl)

I would assume it will also probably detect unsupported hardware and switch to OpenGL automatically but I don’t have any source to back this up.

This email explains it in detail: http://lists.busybox.net/pipermail/busybox/2010-December/074114.html

TLDR: /usr stands for user

/srv stands probably for serve as in serving static files like static websites. (Source)

More information here: https://refspecs.linuxfoundation.org/FHS_3.0/fhs/index.html

The extension is probably not broken because of Firefox but because Flatpak’s sandboxing prevents it from talking to KeePassXC.

Nice