[RedNapalm]

So this is on Firefox Quantum (64.0 64-bit), Ubuntu (18.04.1 LTS) both latest release as of this post.

Before this happened, I could login into the addon perfectly fine but somehow it forced logged me out. I tried to log back in again but upon entering my password, the window disappears the moment I click or tab into the text box.
An alternative solution aside from fixing the window would just to enter the login details within the addon preferences tab in Firefox.

[Jiaz]

This is caused by a WindowManager<->Firefox bug with popups.
github.com/bitwarden/browser/issues/580
you can find more by searching for "firefox extension password gnome bug"

adding login to extension settings is on our todo list