Firefox extracts the paper size information from your Windows printer settings, so that's the first thing to check. In the print dialog, if you click the Properties button and review the dialog for your printer, do you have a small paper size selected and can you update it? If Windows is correct and Firefox is mistaken, you can reset the stored paper size using the about:config preferences editor. (1) In a new tab, type or paste '''about:config''' in the address bar and press Enter. Click the button promising to be careful. (2) In the search box that appears above the list, type or paste '''paper''' and pause while the list is filtered (3) Look for your printer's paper-related settings and then right-click and choose Reset for each (e.g., size, height, width, etc.). If you return to your document and try Print Preview, does Firefox compute the correct size? More troubleshooting suggestions: [[Fix printing problems in Firefox]]