When you say it is downloaded, do you mean you are opening it from the Downloads folder in a different program, not in Firefox? Or is it opening in Firefox?

If it is opening in/printing from Firefox:

Is the Sudoku an image displayed by itself in a tab, or is it embedded in a web page? Usually you can tell by the background: an image by itself usually is on a nearly black background, while most web pages have a light-colored background.

If you view the puzzle in print preview, either

• "3-bar" menu button > Print
• (menu bar) File > Print Preview

can you see the problem there, too?

Does it make any difference to use Shrink to Fit?

Some users have reported that Firefox uses only a corner of the available paper when printing. This can be caused by a problem with the data Firefox has stored about your printer's paper size. If you are having this problem, what kind of printer is it?

Also, could you give us a link to a page/puzzle with this problem? I think that will help in testing it out.

Is this sudoku shown via a plugin like Java or Flash?