Opera is just... ugh. That's about all I can say about it. All this functionality people claim is often inferior to stand alone applications people already have, or so sloppy in use (for instance the included email functionality) that I much rather just continue to use gmail and the simple gmail notifier in Firefox. Additionally, Opera is greatly limited by its extremely poor addon support. Widgets? Seriously, not even close to being useful and the other options.. another ugh.
Firefox does everything you need because it can. It is easily expandable and has great community support. Those features far out weigh the limited immediate functionality benefits in Opera.