Try the reset described here:
http://kb.mozillazine.org/Problems_printing_web_pages#Reset_printer

the edmeister...This reset procedure has definitely not worked for me. I've been trying to repair this for 3 months on my own, not having any personal friends who are Mozilla developers. I even reset every single other Canon/ printer line item back to default, also, in addition to the primary one referred to on the mozillazine page you offered. I began working on the issue from these instructions from the beginning. It makes no difference which of the 2 spots I click to close down FFox, or whether I close out the about:config tab before shutting down, or leaving it up while shutting down FFox. Nor does it matter whether I reboot Window Vista afterward, or not. Or whether I uninstall FFox w/o saving any settings and reinstall it back again. The resets never remain in place, they never "take". Printing web pages with other browsers still works fine, but I like Firefox, except for this, and am not interested in switching. There has to be some solution to this. Can you refer us to someone who can take us further? I see through searches that people have been dealing with this problem at least since 2006. I have W-Vista SP-2 Thanks very much. leapfrog100

leapfrog100,

Sorry you are having that printing problem with Firefox and your Canon printer. The objective of doing the reset is to clear out all the settings for a printer in Firefox, and the next time you go to use that printer in Firefox, it is supposed to pull fresh preferences for Firefox from the printer software.

That reset article does say that it may be necessary for you to reset all the prefs for the printer with the problem. When you clear those prefs and restart Firefox, they should be gone until you attempt to use that printer again - those prefs are supposed to re-appear when a printer is used the first time after the reset.

Other than checking to make sure you are using the latest Cannon drivers for that printer, I don't know what else to suggest. And, I don't know who to refer you to for further help with your problem.

I can say that Canon printers seem to generate more than their fair share of printing complaints with Firefox, and Canon printers seem to have more than their fair share of Bug reports at Bugzilla. That along with all the unresolved Bugs in Firefox makes it hard to know which program is more at fault with problems like this, the Canon print drivers or Firefox. Personally, I have never had a problem with Firefox not printing with any of the three Epson printers I have had in the time I have used Firefox (starting in 2002) or with either of the two Brother printers I currently have.