Opera scores 100 on the acid3 test yet some sites won't work properly on it. It doesn't matter if the browser is standard compliant. If its popular enough web designers will go out of their way to accomodate it.it does not even score 100 in acid 3 test means it is not compliant to todays web standards
The user experience matters more. Firefox has done well with its user generated addon model but I'd rather not worry about user generated bugs slowing my browser down. I still use it for certain tasks because some of the addons add features you won't find in any other browser.