Have you tried the Firemacs extension for Firefox? I use it with Emacs bindings, but I think it should be able to do an approximation of vi bindings as well.
And yeah, Firemacs is awesome. As a matter of fact, it does allow for navigation using some vi bindings by default. Even though I'm an Emacs guy, I find using hjkl a lot more comfortable than C-b C-n C-p C-f. I've heard great thing about vimperator, too.