I just had to do a reinstall of Firefox because it was running incredibly slow. I think I narrowed it down to being a Realplayer plug in, but I am also in the "Firefox is frustrating me" camp.

Another thing that bugs me is that I used to be able to click a folder and choose "Open all in tabs" and it would close all of the existing tabs before opening the new batch. It worked really well, until they eliminated that feature with one of their upgrades. Now I have to manually close all of the previous tabs first before doing so. It's a PITA.