Will it freeze or will it crash? Check to see if any crash reports are generated in [about:crashes] <- clicking on that should open up a new window or tab with "about:crashes" in the url bar.

As for what may have caused this I would first check that the printer driver is up to date.

1. Search for your printer's driver and use these instructions to swap out if you are out of date: http://superuser.com/questions/255699/where-can-i-see-the-printer-driver-v...

Then reset the printer settings in Firefox:

1. Fix printing problems in Firefox

Lastly, you can reset the Applications Settings to change the file to open up with a different program (I do not know if this is happening with only pdfs or all files, including webpages?)

Thanks so much!! Resetting the Firefox printer worked. I had previously tested things in Internet Explorer, so I figured it had to do with Firefox. I did the "about:crashes:, and while I am pretty computer literate i had no idea what any of that code/jibberish was! :)

Thanks again!