Marketshare reflects the perceived usefulness of the product. We're not all sheep.
And that's just for starters.
I tried Opera. I am still on 10.0.5 or whatever because the installer is broken, needed to use the Classic after deleting ALL registry keys and removing every single file. The browser installed, but would quit immediately upon trying to run it. And you think I'm going to have much confidence in a browser so fragile its own installer screws it up? And no message saying WHY it is bombing? Anyway, I tried Opera and got Flash adverts all over the place. Looked around online to discover that Opera doesn't really like the idea of plugins and add-ons. So you have some stuff available by "widgets" (that's like a add-on for people that don't try hard enough) and other stuff by patching in .js files here and there.
Sure, Opera may have an ass kicking response time. But that moment of awesomeness is deflated by all the other things the browser cannot do. Given latency and response times and the fact that I am doing stuff like swapping around a dozen windows and preloading a few songs on YouTube as I write this, speed is relative. You might be able to kick Firefox up and down the aisles using Opera, but when it comes to the real world instead of controlled tests, Opera loses, epically.
A browser that doesn't allow me to filter potentially risky content without it being an all/nothing decision is a security fail (don't even think of arguing PDFs are not Opera's problem - my browser can filter them, why can't yours?). A browser that does not allow *easy* user installed customisations due to a paranoid sense of keeping the browser pure is a feature fail. A browser with this number of quirks (oh, I have not even mentioned the number of times the bloody browser pops up an error telling me a page is no longer available only for me to hit refresh to retrieve said page) is a quality fail.
That's three fails, hence Opera is an Epic Fail. But, you've got me on speed. Go pat yourself on the back. I will, however, carry on using my lethargic Firefox that is sooooooo slow I can feel myself aging because it is a browser that actually does what I want it to do. And it does it well.