Firefox => Chrome
I have just switched from Firefox to Chrome as my default browser on my Linux workstation and, wow. Chrome feels much faster than FF3.5 and despite it still being a beta has been very stable. It has actually been more stable than FF: evil stupid necessary Flash actually works now, where it was totally flaky on FF and would require frequent browser restarts to recover from the plugin crashing. The only things that I really miss are replacements for Flashblock, LiveHTTPHeaders and some nice way to quickly switch proxies. Oh, and if anyone is listening, an OpenBSD port would be great too.
Disclosure: I work for Google, but I don’t speak for them.