I used to have Thunderbird for my email, but since I've now integrated it into Gmail, I don't need Thunderbird anymore. Now I have it installed and configured simply as a backdoor access to my Gmail should the main Gmail interface fail.
For browsing I use Firefox - Chrome wasn't stable enough for my taste (often, when I opened multiple tabs, it would just hang and not do anything for 4-5 minutes, and then fail on all pages and I'd have to reload each tab - really annoying)
I tried the first few versions of Seamonkey when it was started, but I didn't like it. I'm a guy who likes single purpose programs. I don't like it when everything runs from a single program and then when you have a problem with it, everything stops working. Same goes for multi-function apparels (like these combo printer/scanner)