As I use a shared Firefox profile across Windows and Linux, and Windows having been running Firefox 3 for some time, the continual "updating" of Firefox every time I switch OS was becoming tedious, so I decided to upgrade Firefox 2 on my Linux boxes to 3, to get some consistency with Windows.
Consistency is something that I didn't get though. Take a look at the screenshot to the right showing the "Quit Firefox" dialog on both Windows and Linux.
So Mozilla, if you're reading this, please, give us some consistency, it's a dialog, and for some reason, you've mashed up the buttons depending on the OS, and my "Save and Quit" button in Windows has become "Quit" in Linux, and I just lost all my tabs, thanks a bunch!
Another annoyance: To get to the options, using the Windows menu, it's under Tools > Options, on Linux it's under Edit > Preferences. Why do this? I realise it may make the application fit in better with the host OS, but it also makes the application not fit with itself, which is even worse.