Firefox, I guess. I keep that, Safari, and Chrome running all the time...Safari is my blogging browser, Firefox is for development, and Chrome is for fun. Now that I think about it, using three browsers all the time sounds pretty ridiculous.

Funny I use different browsers as well: Opera is for fun, Chrome is for Office tools (GMail, GCalendar, GoogleDocs and so on), Firefox is for work, and Explorer is just for the many Intranet apps and Commercial Sowftware web interfaces that only work right on IE.