I am a long-time pentadactyl user, and was forced to stick with ESR and other 'old' versions of firefox just to keep that addon. I eventually got fed up with doing that last month, so I tried every addon that adds vim-like bindings, only to find that they all suck compared to pentadactyl.
However, I just tried this addon today and it's the closest thing to pentadactyl I've seen so far. I am definitely a fan, and I hope the developers of this addon keeps us pentadactyl users in mind :)
Really amazing work, keep up the good job!