(What an attention seeking title :S)
I find it highly annoying when Firefox allows certain pop-ups to open when I click on form elements such as textfields etc. I also find it highly annoying when it allows windows to resize the browser - nothing like clicking a link and the next second finding the browser in a minuscule rectangle on the top left of your screen. While I'm at it, I also dislike websites using the "_blank" attribute to force a link to load in a new window.
The following are the steps to rectify this: