I have the same problem: after a security update last night on 20.04 LTS, firefox is now completely broken (displays a window frame with no content inside, ie it just copies the background image that was underneath on startup in the framebuffer?).
firefox does work if I pass it a URL at startup.
$ firefox --full-version
Mozilla Firefox 85.0 20210118153634 20210118153634
I have the same problem: after a security update last night on 20.04 LTS, firefox is now completely broken (displays a window frame with no content inside, ie it just copies the background image that was underneath on startup in the framebuffer?).
firefox does work if I pass it a URL at startup.
$ firefox --full-version
Mozilla Firefox 85.0 20210118153634 20210118153634
cat /etc/lsb-release RELEASE= 20.04 CODENAME= focal DESCRIPTION= "Ubuntu 20.04.2 LTS"
DISTRIB_ID=Ubuntu
DISTRIB_
DISTRIB_
DISTRIB_
This is a critical bug for my main browser on the Ubuntu LTS channel!! Please fix ASAP!!!