I'm not sure exactly why but Firefox doesn't handle pop-up windows well all the time. Often times they pop-up and are sized incorrectly so that the windows isn't comletely readable. When this occurs it is sometimes possible to resize the window by dragging the window's edge and resizing it manually, but too often the pop-up window size is locked and can't be resized. It's a significant annoyance but I won't resort to using IE just because of this problem.
The following video tutorial shows how to make a configuration setting within FIrefox that will enable resizing of all pop-up windows. The configuration we will be editing is called:
dom.disable_window_open_feature.resizable