I use the pentadactyl extension for firefox, and I've added the emacs hotkeys <C-a>, <C-e>, <C-n>, <C-p>, <C-f>, <C-b>, <M-f>, and <M-b> to insert mode so that I can at least move between lines and words without much problem. It's not vim, but it makes things like writing this comment a lot easier for me.

Also having <C-p> and <C-n> as up and down means that moving between search suggestions on sites is really easy, which is nice.