[kgroll]

Or for Firefox - vimperator. http://vimperator.org/vimperator

[room606]

Or Pentadactyl - an improved fork of vimperator by it's most active developers. Probably the only thing keeping me from using Chrome as my main browser http://dactyl.sourceforge.net/pentadactyl/

[ElbertF]

Or Pentadactyl, a Vimperator fork: http://dactyl.sourceforge.net/pentadactyl/

[jordinl]

I'm trying it but I don't find the way to enter insert mode... :i, doesn't work, am I missing something?

[scottjackson]

Safari - vim. http://github.com/mutle/vim.safariextension

Only a few keybindings, but I only really use it for the j/k page navigation.

(Note: it does get overwritten by pages with their own keyboard navigation (flickr, tumblr's dashboard, ffffound, etc.))