I think the Firefox snap is broken, something happens with an update (I guess), now the snap does not work, already try the latest/stable channel with 83.0-2 and the channel esr/stable 78.5.0esr-1 both crashes with the following error:
Yesterday the FireFox snap was working great, now just crash, does anyone else have this problem with the latest/stable channel or the esr/stable?
I manege to fixed following this https://askubuntu.com/questions/1224125/font-characters-displayed-as-squares-in-ubuntu-18-04
I just uninstall the snap then I update local font cache and that fixed for me.
I would leave this here, maybe someone face the same problem.
how fonts get corrupted like that even without the user doing anything?