Do any pages print normally or does this affect all pages?

Can you view the page in Firefox's Print Preview? This is available when you click the "3-bar" menu button and then Print, or using the File menu > Print Preview (if you do not normally display the menu bar, tap the Alt key to activate it temporarily).

In Print Preview, check the Scaling setting on the toolbar and if it isn't set to Shrink to Fit, try that to see whether it helps.

Occasionally users report that Firefox is using an incorrect paper size for their printer -- it thinks your printer has tiny paper. This may be hard to detect from Print Preview, but is apparent on paper, where only a small area in the upper left is used, or if you print to a PDF document, and open it in Adobe Reader and check File > Document Properties to see the paper size.

If Firefox is not using the whole sheet of paper, this can be caused by Firefox having extracted the wrong paper size settings from Windows when reading the print driver data. Clearing it can involve finding some obscure settings, but here goes:

(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 above the list, type or paste print and pause while the list is filtered

(3) For each setting that specifically mentions the problem printer, right-click and Reset it. The fastest way is to right-click with the mouse and then press the r key on the keyboard with your other hand.

Note: In a couple threads involving Brother printers, the preference printer_printer_name.print_paper_data was set to 256 and when the user edited it to 1 that by itself fixed the paper size problem. If you use a Brother printer and see a 256 there, you can edit the value by doubling-clicking it or using right-click>Modify.

Any improvement?

The Scale preference controls the size of what is printed.

Scale is available in the Print Preview window and also available in File > Page Setup.

Shrink to Fit or 100% usually works best.