I've been using Mozilla for the past several years, and like it. Never tried Opera - has anyone any comparison opinion on Opera vs Mozilla latest versions?
I keep MSIE for those websites that won't work with a "generic" browser, like the AIS and Met Office sites.
Mozilla does everything I can think of that I want in a browser/mailer package. What I particularly like is that it knows to use my spamcop.net address when posting to newsgroups, so I don't get my primary e-mail address harvested by the spammers. That's a neat feature.
I can also switch addresses after I've written an e-mail - it offers all the ones I have set up in Mozilla to pick from.