Running Steam Proton Games in Firejail
Proton by Valve has greatly increased the number of playable games on Linux, but almost all games running in proton break when Steam is run from firejail.
A couple fixes can be introduced to allow Proton games to run, the errors referred to here come from running Steam from a terminal and watching the feed (just type "steam" into a terminal and hit 'Enter').
#/usr/bin/env: 'python3': Permission denied
Edit /etc/firejail/steam.profile and add the line:
ERROR: ld.so: home '/home/user/.local/share/Steam/ubuntu1232/gameoverlayrenderer.so' from LDPRELOAD cannot be preloaded (wrong ELF class: ELFCLASS32): ignored
Edit /etc/firejail/steam.profile and comment out "seccomp" with "#", like so:
This will expose a lot of kernel surface area, reducing the effectiveness of Firejail in protecting the remainder of the operating system from a compromised steam client or a game launched within it. You have to decide if it is worth the games you are playing.
Also consider not playing games on a machine that needs security, you can always buy a chromebook for banking or shopping.
A more open seccomp filter could be generated by running strace on steam, but I am too lazy to do this myself. I once tried, but the syntax of Firejail was undocumented and a lot of syscalls I tried to add to a whitelist from strace were considered invalid to firejail.
Additional problems can sometimes be fixed by removing the steam overlay for a game.
Hope this helps someone; Glory to Linux