Wow - that's brilliant. I have used firefox + pentidactyl for ages, on and off, but usually end up removing it as it mucks up web dev stuff too frequently.
But this for a daily browser and then firefox for heavyweight stuff looks cool.
FWIW, I'm currently trying out VimFX (largely because vimperator has yet to be ported forward to work with latest firefox nightlies) - and while I'm not certain I like all the decisions the project makes (I probably want more of a vi(m) monster) - the project is well thought out, and the decisions are motivated - not random. And it appears a much simpler, more compact and self-contained project that vimperator/pentadactyl (note, I've only seriously looked at modifying VimFX - and the dev documentation is excellent):
But this for a daily browser and then firefox for heavyweight stuff looks cool.
Thanks!