Reset the page zoom on pages that cause problems: View > Zoom > Reset (Ctrl+0 (zero); Cmd+0 on Mac) See Font size and zoom - increase the size of web pages and Font size and zoom - increase the size of web pages and http://kb.mozillazine.org/Zoom_text_of_web_pages

If you mean with printing then adjust the print scale: File > Page Setup > "Format & Options": Scale (un-select: "Shrink to fit page width") See http://kb.mozillazine.org/Problems_printing_web_pages and How to print web pages in Firefox

I was in the middle of writing something and accidently made the page really small and I had no idea how to get it back and was getting frustrated when I checked here and found a solution, this was very helpful thank you. All fixed now.

resetting size does not work for me. I've tried them all..... 100% then half the page is missing - everything shifts to the right. SHRINK TO FIT is so small I need a magnifying glass to read. This just started happening. i changed nothing to make this happen. How can I fix it

If it is about printing page then check the print scale setting.

File > Page Setup > "Format & Options": Scale (unselect: "Shrink to fit page width")

See also http://kb.mozillazine.org/Problems_printing_web_pages and How to print web pages in Firefox

It happened to me too....

In Mozilla Firefox go to VIEW ->Zoom (then choose to 'zoom in' or 'zoom out'

The 'Reset' may not do anything.

Hope this helps.

My Father had this problem small printing of emails through Firefox. This solution helped us.

If you are having a problem with Firefox printing only on a small portion of the page:

Press {Ctrl + P} on the keyboard and verify the correct Printer is selected, Click the Properties button and look at the Paper tab and Layout tab (or whatever your particular printer brand calls those items):

Paper: Is the correct size selected? (usually 8.5"x11" or A4). My Father's was user defined, we changed it to letter size. Is the Orientation correct? Is the Printable Area correct? Layout: -Is Reduce/Enlarge check-marked? It shouldn't be. Is Multi-Page check-marked? It shouldn't be unless that is what you want.

Try this,

Press {Ctrl + P} on the keyboard and verify the correct Printer is selected, Click the Properties button and look at the Paper/Quality tab and Layout tab (or whatever your particular printer brand calls those items):

Paper: Is the correct size selected? (usually 8.5"x11" or A4 or Letter). My Father's was user defined, we changed it to letter size and that solved the problem.