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.

  ____________________

  1. https://github.com/akhodakivskiy/VimFx