Rated 5 out of 5 stars
Even if I wasn't just looking for a way to smugly use Vim hotkeys and commands in Firefox, Vimfx would be a great addon. It legitimately allows me to more comfortably and efficiently use Firefox.
It's so well put together and polished. Probably the only addon I've ever installed where I wasn't thinking of ways it could be improved while using it.
This little addon might just force me to switch to Firefox ESR.