Fast forward to last week and I'm considering switching back. It's not because of any sites that Firefox hasn't supported. It's because I recently needed to start using a webapp to access to email from $WORK. They locked up email and now my local Mail.app client won't connect to $WORK.
My preferred way of handling this is to wrap the webapp as a desktop shortcut, so the entire site is wrapped in it's own window, etc. I also have a couple of other work webapps that I like to treat as applications. Chrome makes this easy/possible. Firefox does not.
This used to be something I did with Firefox, but now, it's not possible (or at least easily, on a Mac). Firefox was something you could embed. And now, I have no idea.
Small little features like this are where Firefox starts to lose users. Right now I have both running, but I can't see that lasting long.