Pentadactyl/Vimperator will soon stop working, I believe at FireFox 57. Firefox is removing the ability to run XUL extensions, which will effectively be the end of the awesome VIM plugins for FF :(
I've recently made the switch to VimFX as a result of this and I have to say I couldn't be happier - it may not have some of the more powerful features (that I'm unaware of) but it definitely gets the job done.
I also switched to VimFX from Vimperator, and it blew my mind how much faster Firefox suddenly became! I used to simpathixe with my friend who switched back to Chrome "for it's speed" but without Vimperator, Firefox is waaaaay snappier than Chrome (on my machine). It made browsing a fun tactile experience again!