I have been using Firefox by Mozilla for a week now, and really love it. It’s fast on my pokey 266mhz Windows98 laptop, and amazing on my 2.4ghz XPpro machine. It has most of the features of Opera, such as popup blocking and tabbed layout, but it seems more lightweight and streamlined. I don’t need Opera’s chat feature or mail client, and if I can save some vertical space by not dealing with the ads, that is a bonus too. (especially on my 800×600 laptop)
I am also now using Thunderbird by Mozilla for my email client. My server is configured as IMAP4, so I can pretty much use any client I want and get the same experience. (Except perhaps Opera, which seems to have a couple issues with IMAP at the moment) Like it’s counterpart, Firefox, Thunderbird is a stripped-down app, and runs fast and doesn’t have all the bells and whistles. Just simple, clean design, and great performance. I used to use Mozilla 1.7 for email, which is very similar, but figured I’d get rid of the Mozilla “suite” and do Firefox/Thunderbird instead. Mozilla has a chat feature, I think, and html composer which I will never use, so why install it?