Everyone complains about Firefox printing problems year after year (it never worked). My suggestion would to be if it doesn't look right in Print Preview use the "Launchy"extension to bring up the page in another browser and print it from there. I'm still doing most of my stuff in Firefox. (Actually I seldom do any printing at all)

Launchy :: Add-ons for Firefox

Launchy will enable you to open links and mailto's with external applications..."

• https://addons.mozilla.org/en-US/firefox/addon/launchy/
• http://dmcritchie.mvps.org/firefox/firefox.htm#launchy

No upgrade goes unpunished. After upgrading first to Firefox 4, then to 5, now I can't print any web pages. Prints from Word or any desktop file just fine. Went to Safari and it prints web pages with no problem. (iMac running 10.6.3)

I had success with this: Reset printer

As a first step, reset the selected printer in your Firefox preferences:

   Type about:config in the Location Bar and press Enter. A list of preferences will appear.
   Find the preference print.print_printer (Note: this preference is missing in Firefox profiles where you've never used the printer.)
   Right-click (context-click) that preference and select Reset. (Some users may need to reset all the print.printer preferences for a particular printer, if resetting this one master preference doesn't solve the problem.)
   Restart Firefox and see if the problem is resolved. 

Note: If you get the warning dialog, "Printing failed when starting the document" and if the print.print_printer preference has no printer shown, either you don't have a printer selected, or Firefox doesn't know it is installed on your system.

It's from mozillazine