the only thing keeping me from moving completely from Firefox to Chrome is Pentadactyl (http://dactyl.sourceforge.net/pentadactyl/), and better greasemonkeyscript-ability. Firefox on Mac has always had memory hogging issues, but I really can't live without my vim overlay (I've tried the Chrome alternatives, like vimium, but they pale in comparison)

As people have said about Firefox's hackability, I don't think there will be a Chrome extension as good as Pentadactyl.