Firefox is supposed to "remember" the last used printer, and use that as the "default" until you select a different printer.

First - make sure Firefox is still set to "remember".
Type about:config in the URL bar and hit Enter.
If you see the warning, you can confirm that you want to access that page.
Filter = print.save_print_settings = make sure that pref is set to true

If that isn't the problem, try resetting all the prefs for the "WPB" printer and see if Firefox then saves the change to the "NYC" printer on the first try.
http://kb.mozillazine.org/Problems_printing_web_pages#Reset_printer

Thank you for the support assistance. However, this morning when I tried to use the NYC printer to print an email the Firefox dialogue box defaulted to the NYC printer which it failed to do all yesterday. It appears to me that there is a 24 hour delay in recognizing the switch in printers.

Nonetheless, I followed your instructions and typed "about:config" in the URL bar and hit Enter. The "print.save_print_settings" was set to "true".

(I could not check the WPB printer because I am not there and if I changed the default it still will not print to it because that printer is not connected.)

Is there a built in time delay in recognizing print preferences separate from the number of times of print function use?

No delay, as soon as you select a different printer and use that printer, Firefox should use that one the next time automatically.

Well Firefox is not following it's program because the browser finally defaulted to the last used printer yesterday morning after some 20 print jobs two days ago where it refused to do so and had to be set manually each time. This is not the first time this has happened to me. While I confess my situation is somewhat unusual in that I have two printers of the same model in different locations , they are separately named in the "devices & printers" folder in Windows 7.

Is there an answer to this glitch?

How about changing the printer and printing something, then close Firefox and then restart your operating system? See if that helps ....

I am curious why you need two separate versions of the same printer installed. Is one used on a USB connection and the other part of a network configuration or wireless? If both are network or wireless, are they using a different IP address on the network they are on?

The only time I have seen a similar problem with Firefox not wanting to default to the "last used" printer was with a USB inkjet and a network connected laserjet (Brother) - the laserjet would go to "sleep" (energy saving mode) and Firefox would switch to the inkjet every time the laserjet was asleep. That problem was eventually solved when the USB inkjet was replaced by a "network" connected inkjet - still can't understand why that made the difference, though.

I guess you missed the purpose of the two printers. One is in New York City and the other in West Palm Beach. I take the laptop to West Palm Beach and hook up to work. When I return to NYC I connect to the NYC printer. I actually have a third printer of the same model in another location which has not yet been used with this computer but will be used in March. I can only try your suggestion when I go to WPB at the end of the month. Then when I connect the WPB printer and it does not default to it after the manual change I can shut down and reboot and see if that solves the problem. Remember, this problem only exists with emails - not with wordprocessing or pdf documents.

Sorry, the same model printer in two different locations really shouldn't need two separate sets of drivers and thus appear as two separate printers, barring the need for different preferences settings (like one used with A4 paper and the other with letter size paper) or a different network IP Address. I don't understand why you think you need both and why the "wrong printer" doesn't work, unless you left something out of your explanation of this issue.

Maybe another support helper will have some additional ideas.

I have one set of drivers for all three printers. The third has not yet been connected so it does not yet appear on this laptop. I had three on my prior laptop. Each time a new MFC 7340 is connected it shows up in the Windows "devices & printers" folder when it is initialized. This has been discussed with Brother tech support. Additional drivers are not required. So currently I have two of them in "devices & printers" but only one is connected at any one time. There is no problem switching with Internet Explorer - only with Firefox!