1) I would say they're about equal, if you couple Firefox with the NoScript Extension your ahead in terms of Security. 2) Opera renders faster particulary going back and forward between cached pages, Firefox is going to have this (enabled) in the next version. Otherwise they're about the same imo. 3) In my experience with Opera it crashed when i would open alot of tabs, that happens often when im reading wikipedia. Firefox has never crashed on me. Firefox is updated more often i would say. 4) No Idea, I just use the default theme. 5) I use Firefox, whats a popup? 6) The Adblock Plus Extension for Firefox is extremely powerful, Filterset.G is updated often and blocks nearly everything. 7) Windows Media, Quicktime, and Real Plugins work fine with Firefox, never needed to play with it. 8) Firefox is compatible with more Websites than Opera. Please check out the Firefox Extensions in my signature, they're excellent!