Since I spend most of my time in Vim, I moved from Chrome to Firefox just for Pentadactyl which brings Vim bindings to Firefox, and it's much more powerful than similar Chrome add-ons. Tabbing between Vim and Firefox, sharing keybindings, and never touching the mouse have boosted my productivity tremendously.

You should see how many more HN articles I can read per hour.

I'd add Guake (or whatever the Mac equiv is). Ctrl-Spacing a universal, auto-focusing, half-screen terminal window at any time is a great tool. Right now, I have my whole Tmux/Vim/RailsServer/irssi/ssh command center in the Guake terminal that can be toggled whenever. Alt-tabbing is unmanageable.