Hmm, you're right about Seamonkey - should've thought of that one. The number of derivatives of Firefox is kind of overwhelming. I did get iceweasel though!

Yeah, I was a bit surprised you listed iceweasel which is basically just a rebranding of firefox and forgot seamonkey, which is much more different since it is a suite (with an email agent and newsreader, a composer and probably one or two more things). Even if at the moment I only use it as a browser, my folks use it for mail too. I don't know if it is still the case, but at some point, seamonkey mail+web browser were lighter (RAM-wise) than firefox (let alone firefox + thunderbird).