I know you might not be interested in anything chromium-based since this thread is about firefox, but qutebrowser[1] is a great solution for anybody looking for vimium/pentadactyl-like experience.
qutebrowser on the other hand seems to have limited support for addons and the builtin features are good, but not on par with what addons can give you (https://github.com/qutebrowser/qutebrowser/issues/28).