You might have already seen this tip on Lifehacker recently, but I felt it was important to spread the word on how to stop web sites from Resizing your browser (One of my pet peeves).

Just open up the Firefox Options window, and click on the Content tab.

Click the Advanced button across from the “Enable JavaScript”, and you should see the “Advanced JavaScript Settings” dialog.

From here, you just have to uncheck the “Move or resize existing windows” checkbox, and you are done.