I have the same problem https://support.mozilla.org/en-US/questions/1421734 it's not a pdf. If I want to print a shipping label from eBay using Firefox nothing happens if I try to make it bigger. I can make it smaller but it is too small to begin with. If I use Brave or Edge (using the same printer) it works I can adjust it and make it bigger up to 200 %. I have already reset the printer options in Firefox and tried when disabling all add-ons.