Safari -> Firefox
I just realized today that one of the changes I made when I switched from Debian to OS X on my desktop is that I started using Apple's Safari browser instead of Firefox. I like Safari. It works very well, though Safari, Firefox, and Chrome are all world-class browsers. But only Firefox has Certificate Patrol, which makes it a little easier to notice man-in-the-middle attacks on the SSL infrastructure. So, in order to restore that, I've switched from Safari back to Firefox.