One major annoyance between the Mac and PC versions of Firefox 3 is the position of the “Done” button on the Add Bookmark dialog. On a Mac, the button is on the right. On a PC, it’s on the left. I won’t comment on which is better, just that the difference breaks my muscle memory and is driving me up the wall, and causing me to lose bookmarks that I think I’ve saved.
The only saving grace here is that “Done” is the default action on both, so what I really need to do is train myself to press Enter on the keyboard instead of mousing over and clicking on the button.