Can you describe this problem in more detail. Is the problem that Firefox won't show the Print dialog, or that portions of the printout are blank/missing, or that you get an error when trying to print?

Since the problem occurs on particular sites, could you give the addresses of a page with this problem? For email, you don't need to post the address of your email, but please mention the name of the site (e.g., Yahoo, Hotmail, Gmail, etc.)