I too think Opera is a pretty good browser
I read a post recently by Jonathan Ellis that I've been meaning to write myself for a few months:
I've been trying Opera 9.2 for a week, and I'm pleased with it enough that it's going to continue to be my main browser. The main selling points for me are
* MDI weirdness is mostly hidden now, I hated earlier Opera UIs
* 20-30% less memory use; even after poking about in the guts of about:config to force FF's memory cache to the same 10MB that I gave Opera (which exposes this option right in the UI), Opera consistently uses less memory for the same workload. (Without adding this option to FF, it would max out around 400MB instead of 150MB.)
* feels snappier; opera seems quicker to start rendering something useful on slow-loading sites like 1up.com, although total render time is about the same. It's also instantaneous to open a new tab, which consistently takes around 1s on FF after I've been using it a while. I open and close tabs frequently...
My firefox2 memory issues have also moved me over to Opera. The only things I use FF for are google docs, and whenever I need to use the FireBug, WebDeveloper, or Selenium IDE extensions ( oh - DocuFarm is awesome too) or whenever else I hit an opera-unfriendly site. Okay, so I'm not exactly firefox free ... but I try to keep the tab count down to about 5 or so. When I have to do research and open up 10 pages of doc's / google results it's definitely Opera that I use.
I suspect it's not entirely FF2's fault, but the very extensions that I'm infatuated with are part (the cause?) of the problem. I installed the latest FF3 Alpha using Altiris (ditto Safari/Windows - I love Altiris) and while extension-free, it's pretty darn fast ( faster than ff2). Over the course of a day, the memory footprint is much better too. I'm hopeful the release reflects this, and I can winnow down my browsing choices, but until then I feel like it's not the worst thing in the world to better acquaint myself with cross-browser rendering behavior.