What type of printer - is your system "default printer" a laser-jet that has a sleep mode or energy saving mode?

Local USB connection or a network printer?

The "default" in Firefox is the last used printer, regardless of which printer is set as the system default printer. IOW, Firefox should use the same printer for all print jobs until you change to the other printer and keep using that one until you change it again. Sometimes the "last used" won't be used if that printer has gone to sleep, or if a network printer that is used my multiple PC's is the "last used". Also, if the "last used" from a previous session isn't turned on, Firefox won't warn you - it will use whatever is turned on and available. Basically, you need verify the printer you intend to use is the one that is selected when more than one printer is connected, especially when a network printer is connected.

I have an inkjet connected local via USB and a network laser jet on my small LAN at home, and on occasion I have had a Firefox print job that I expected to be printed on the laser jet, which I had last used 10 minutes before, go to the inkjet instead. Now I make sure I look at the Printer - Name dialog to verify which printer is going to get a print job, when I have both printers turned on.

Thank you for your response.

The default printer is a Samsung Laser printer that doesn't sleep. The other printer is an HP colour jet. The laser is connected via a USB port to my router and the HP is hooked up via a LAN cable the router. The printers are shared with other computers.

This problem only started recently. I had no trouble printing to the laser for the last many months.

No matter how many times I select the default printer (laser), Firefox always returns to the HP printer for the next print job. It is a pain to now have to select the laser printer every time I print. Since you appear to have to do the same thing (select the correct printer), there must be a bug in the software.

Try the reset described here for the print.print_printer preference:
http://kb.mozillazine.org/Problems_printing_web_pages#Reset_printer

"print.print_printer" had the colour printer in the 'value' column. Clicking 'reset' cleared it. Firefox is now printing to the laser printer without being selected.

Many thanks for your help - the problem is solved.

Note that NONE of the replies answer the original question.

The key word in the question is "Why" and "default printer" refers to the system's default printer.

Why does Firefox behave differently than any other Win app when it comes to printing, ALWAYS use the system's default printer UNLESS the user changes it (and NOT memorize the choice).

To put it another way, Firefox should NOT always use the last printer selected.

This non-standard printing behavior should be changed.

bhorne - Have you select your default printer on your system?

@Tecknomage

Who the hell knows why. The printing code was written by Netscape long before the Mozilla Foundation was even created 14 years ago, and I doubt if there are any of the original programmers around any longer who could answer why it was done that way. My guess is that it is a result of providing cross OS support, as I have seem similar quirks with some other open source programs that are made for Windows and Linux, and maybe Mac, too.

print.save_print_settings can be toggled to false to have Firefox not use the last used printer as the "default" in Firefox.

Now THAT works (print.save_settings false)