Firefox is much faster than firefox, it leaves more room for browsing too. You can remove all of the toolbars if you need, giving you nearly a whole screen of browsing space. Opera is bulky and horrible.Aside from the highlighted mistake, upon which it would be pointless to loiter:
Viewable page areas, with tabs, as minimalist as I could make Firefox and nearly as much as I could Opera (whilst keeping them both usable):
Opera: 0.676Mp
Firef: 0.641Mp
Hah.
I'm all for freeware (heh, like Opera), and Open Source is great. I use Thunderbird. I remain firmly convinced that Opera really is better.