Firefox for browsing (because the awesomebar is still way better at finding things in my history/bookmarks than Chrome for me, and because of bookmark tags). Chrome for development.
I occasionally find myself using chrome for browsing because I find it that much more reactive and stable than firefox.
but I couldnt leave firefox for developing, as much as I have tried I just always find the web inspector lacking compared to firebug
Also how recently have you tried the Chrome inspector? It's been getting a lot of attention lately from the dev team.