The fact that Opera does so well on Acid tests may actually be to its detriment.
I'm primarily an Opera user, and I can say with a great deal of confidence, that most websites are not built to render properly according to standards. If I were not a web developer, I wouldn't understand why every site I visit renders wrong and would switch to a browser that shows them "properly".
I appreciate it as a web developer, and because I like standards, but even then, the developer toolbar for firefox means that I do most of my work there and most of my personal browsing in Opera.
As an Opera user, I don't recognize this at all. Most sites work fine with Opera.
Only problem I have is Flash. But that actually works a lot better in Opera than in Firefox. At least when it crashes in Opera, only Flash dies. If it dies in Firefox, the browser dies.
Don't Firefox also get money through content partners (eg: Google Search?).
I'm aware that you have had to pay for Opera before - Wii points on the Wii, and also for the DS/DS Lite version of the browser.
Opera have always been at the cutting edge of web-standards. They're always good with the ACID tests.
There mobile versions are excellent and render stuff quickly and efficiently on all the mobile phones I've used and played with.