I'm going to ask you to reset your printer settings in Firefox. The steps may be unfamiliar, but it's not difficult. First, press Ctrl+t to open a blank tab, type about:config in the location bar, and press Enter. Click the button promising to be careful. Second, in the Filter box, type printer and wait a moment until the list is filtered. Third, find '''print.print_printer''', right-click it, and choose Reset. Then test again. While you're in about:config, you may notice settings for paper_height and paper_width. You can edit these if you like, but I think Firefox will override your changes based on information extracted from the printer driver. Any luck?