Not sure what's up for you, seems to work for me and everyone else... ¯\_(ツ)_/¯
Yeah Im seeing that if you export a godot game on itch it just doesnt work for firefox on linux (website limitations for what i undestood), so I just have to play on another browser for now (very nice game btw!)
Uh... I am on firefox for linux and it works for me... (arch btw)