Fx
isn't freeware, its open-sourced. Software is different then real life Ren. The Mozilla Found. is just a great group of people giving back to what is owed to us...the community.
Opera on the other hand is NOT free, it is supported by ads.
You may not care about a theme, but many other users does. It adds your own taste, you, into your browser. Sure there is Opera themes, but Fx are by far prettier then Opera's IMO.
As far as the extensions go, that is simply not true for Fx. If Mozilla finds that one is unstable or causes problems, they yank it from their website, so it certainly does not cause stability issues. As for it slowing it down, that is not true either. It may cause a second or two more for the initial loadtime of the extension but that is probably it depending on the type.
Internet Explorer is still the top dog, but the fact is that Netscape has been knocked out. I do want to inform you Ren that Netscape and Fx are almost the same code! Fx is just a heavily modified but its still based off of the same engine.
If I can recall correctly, Fx is currently beating Opera in its' total share. Oh and it also had a bigger debut then Opera 8 (beta) did

. Although I love Opera, and any alternative to IE, Fx still is the very best in my mind, and probably always will be unless a major change happens in the market...dare I say GBrowser? :eyespop: