• Click the Firefox menu (the one with 3 horizontal bars)
• Pick Print, you'll see a preview of how the page will look.
• At the top of the screen, click Page Setup
• and then click onto the "Margins & Header/Footer" tab. 
• Look for the drop-down box which says "Date/Time" or "URL" or whatever is setup for the Header and Footer and change it to "--None--".