I brought this up on the desktop list a few months ago, when the
plugin that was shipped with Fedora stopped working. I got the
_impression_ that the recommended way to install GNOME Shell
extensions is via gnome-software.
In any case, the "chrome plugin" works with Firefox despite its name.
P.S.: Gmail keeps blocking my attempts to reply, I may have
inadvertently spammed the list with multiple identical messages.