In the "native print dialog" box, what you see when you do {Ctrl + P}, make sure the printer is selected. The "default" in Firefox with WinXP is usually the "XPS printer", until you select a different printer. Once you have selected a different printer, that will be the "default" until you change it to something else. Firefox doesn't go by "system" setting with that pref, it keeps track of the last used printer.

OK-I really appreciate the ideas that were put on the table.

Here's the truth!

To fix the issue: I needed to go into XP and recover to a date prior to the issues occurring. Whatever happened will remain a mystery. The printer now shows up and is fully functionable.

Thanks for your time and Clear Skies-

To the respected guru the-edmeister, et al. - In my case, this "issue" precludes the suggestion for fix above, because we never see the Print dialog following CTRL+P. What we get on every CTRL+P or File>Print Preview or File>Print... is imm. the Windows error dialog box with similar text as nestle2 had. See attached Img01, which on clicking 'Yes' was always imm. followed by Img02 attached. This began, imm. after I had uninstalled Firefox 3.6.16, rebooted, then via IE 8.0 downloaded Firefox 4.0 installer, then installed Firefox 4.0 and rebooted. Also have added a few extensions that I used with v3.x, most notably NoScript. Never had this issue to happen with Ffx 3.x and extensions. OS = Win XP Pro (x86) SP3, fully patched. In last few days, accepted all 15 of M$'s Automatic Updater-pushed patches from April's Patch Tuesday, and also their Silverlight update yesterday, with no visible change in this "issue." Have confirmed via services.msc and msconfig that the Print Server service is "Started" and "Running". Also, Win Task Manager > Processes tab shows spoolsv.exe with User = SYSTEM, PID = 1852 and Mem Usage = 8,404 K . Yes, other apps can print normally, including Wordpad, Notepad, and Open Office v3.3 Writer. Please advise how this enthusiastic Firefox adopter can force Firefox 4.0 to recognize the Print Spooler service, running in Win XP. Your assistance will be much appreciated.

Should perhaps have added that my system is an HP Pavilion a1020n with 130 GB free on system partition in which both OS and Firefox are and were always installed, upgraded to 2 GB RAM two years ago. Also, am running COMODO Internet Security Complete 2011 for firewall and AV and M$ Security Essentials for anti-spyware too, with their current updates; these were disabled during the installation of the Firefox 4 Setup, and they restarted when rebooted after the installer reported itself complete. Ffx 4.0 created a totally new profile for itself with a new "name." I have NOT tried to restore my former profile, bookmarks, etc., but I would like to do that after we solve this problm. I looked at about:config and it showed many, many lines addressing my printer's configuration there, including this:

Name = "print.print_printer" Status = "user set" Type = string" and Value = HP Laser Jet Professional P1102w on WiFi IP 172.16.0.247". This Value is the same Name that I set for this printer in Windows' Printers & Faxes. I do not recall - but might have been so tired late at night as to have a memory fail on first try - ever printing successfully with 4.0 - and I did not change anything in about:config.

However, I do not feel competent to tinker with these parameters myself. And, I really am hoping not to have to waste 5 or 10 more hours to try various Restore Point dates and then reinstall and repeat configure all that stuff. I would much prefer to have suggestions for correcting this bad behavior of Firefox 4.0. All well-meant recommendations will be appreciated. [Maybe I had better try posting this as new question, for a much-needed, rapid response]

Is FallingRocks question ever going to be answered? There seems to be about 25 people with this exact problem, including myself, with no response?

Is it time to move to Chrome?

Before you can perform printer-related tasks such as page setup or printing a document, you need to install a printer. Do you want to install a printer now?

yes

Operation could not be completed. The print spooler service is not running.

Here is how I was able to resolve this problem.

I first made sure I had downloaded but not installed the latest Firefox setup file.

Go into Add/Remove programs and uninstall Firefox but keep your Personal Data.

Locate where the Firefox was originally installed, usually C:\Program Files\Mozilla Firefox and rename this folder.

Locate the Firefox setup file and reinstall the program again, this resolved my problem. I hope it fixes yours.