My one gripe about using OSX is the Firefox browser. There's not PDF support for it, meaning that I can't open PDFs in a window, but instead I have to download it. That's just ridiculous.
And then there's Safari, which can handle PDFs, but then it doesn't have mouse gestures. Are you kidding me? That's a necessity.
I predominantly use Firefox. But because i'm using Adblock, some video sites don't work (and i can't for the life of me figure out how to unblock them) so I have to use Safari.
This is one of the two things that I hate most about OSX. Something so simple, yet so overlooked.