I print on different including a receipt printer with roll paper.

I had to reset Firefox yesterday because of a bug, and then changed the Printer Properties to be able to print again in the right format on the receipt paper. But now everything I print from Firefox (even when I change the paper size to Letter on the Printer properties for the regular printer) is in the receipt paper format (long and narrow.) When I do Print Preview, I can see that the paper looks like the roll paper, even if I'm trying to print on letter size. I tried resetting both printers with about:config, I tried changing in the printer properties for both printers and nothing works. Is there a way to change the default paper size in Firefox?