Linux is not an operating system for the unwashed masses, it's a specialist operating system for more technical oriented folks. It's less polished in many areas and requires some jumping through hoops at times as we all know. In return, you get a vastly better user experience if you're the right kind of user.
Whenever I am placed in front of a standard Windows install, I'm shaking my head in astonishment and wonder how people put up with that. Yet, if I were a standard Windows user placed in front of a linux machine, I'd probably do the same.
We're just a different species of users. If linux users cared as much about browser specifities as they did about other things, I'm sure they would already be fixed. But the truth is: as a long-time linux user I can state that Firefox is just fine. Really, it is. For me. And probably for many other happy linux users too.
Does that mean if couldn't be improved? Of course not. But show me the software for which you couldn't say the same. Okay, maybe Emacs. Just kidding.