Have you tried changing the print scaling in Firefox? If that's set too low, what you are printing won't fill the entire page.

Try the follow:

1. Press the ALT button on your keyboard and some options will appear at the very top of the screen.
2. Select File
3. Select Page Setup

Generally, the scale should be set to 100% or the Shrink to fit page width option should be selected.

You'll probably also want to check the margins. They are usually set to 0.5 inches on all sides.

Hope this helps.

P.S. The address bar is the search bar at the top of the Firefox window that has the circle i icon, the website address and the star icon in it. Just figured I'd mention it since you referenced it in your question.

A different reason for this problem is if Firefox suddenly things your paper is 1/4 of the usual size. This can be caused by misreading printer data. As a possible quick fix, try this:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful or accepting the risk.

(2) In the search box above the list, type or paste paper_data and pause while the list is filtered

(3) This value varies, but based on past threads:

• 1 means letter size
• 9 often means A4 size
• 256 is an unknown small size that sometimes shows up on Brother printers for no apparent reason

To edit a preference, double-click it to open a small one-line dialog box. Modify and click OK.

Any improvement?