VimFx[1] is awesome. Let me quote the important part from its
description:
In my opinion the problem with Vimperator is that it has too many
features and aggressively changes the default Firefox appearance and
behavior. Vimium was developed for Google Chrome and it was exactly
what I needed in terms of added functionality. That's why I decided to
develop similar extension for Firefox.
VimFx will be nice to your browser and to your habits. Promise.
Exactly. Vimperator or Pentadactyl are too invasive. I don't want to
turn Firefox into something else, I just want to extend it. That's
what VimFx does.
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1.
https://github.com/akhodakivskiy/VimFx