See this:
http://kb.mozillazine.org/Problems_printing_web_pages

Thank you. "about:config" log does not list any print.print_printer. However, listed are approx. 40 items "printer_HP_Officejet_Pro_L7600_Series.print_", all user set with various types and values. Also listed is print_printer, user set, string, HP Officejet Pro L7600 Series Previous to upgrade I didn't have any problem and now I can print SOME web site pages, so the printer has been used in FF before. Can I supply you more information that would help?

Is that printer selected in the Printer - Name box?

see the screenshot

YES, it is.

If it is selected there, the print.print_printer pref should be there and have that printer name to the right in the Value column.

Do a reset of all the prefs for that printer, as described here:
http://kb.mozillazine.org/Problems_printing_web_pages#Reset_printer

I 'reset' the pref called print.print (which is the pref that is the closest name of your recommendation) restarted FF and now that pref is not listed. As stated, I have 40 pref names printer_HP_Officejet_Pro_L7600_Series.print_* 15 pref names print.print_*

4 pref names  '   print.*'   You said to do a reset of all prefs for this printer but I am a little "gun-shy" to mess with so many prefs.  Is there some way you could look or I could provide you the "about:config" list? Would that be helpful?

the-edmeister: regarding my last reply...should I go ahead and "reset" ALL of my printer preferences?

TO: the-edmeister: I may have found a solution to my "inability to print from websites" problem. I reset all prefs that started with "print". No change except the 40 prefs listing my HP printer were missing. Still no "print.print_printer" in log and still unable to print. I looked at my Add-ons...although the Bing Bar was disabled, an add-on called "HP Smart Web Printing 4.60" was listed and researching it I found it was for IE only. So, I disabled it and am now able to print from the websites I need to. BUT, still no "print.print_printer" in about:config log. I have a "print_printer" pref, listing my HP printer. So I hope I'm okay now. I am confused about my add-ons, some programs from my security, Kaspersky and NoScript are noted as incompatible. Any response to this reply would greatly appreciated as I learn as I go and you have given me some great insight to how things work. Thank you, Linda

print.print_printer should appear after you have printed something. If printing is working now, don't worry about that pref.

HP Smart Web Printing hasn't been compatible with Firefox for a few years now. IIRC the last time HP updated that application was for Firefox 3.5 and nothing newer, it shouldn't have been enabled in Firefox 9.0.1. HP shouldn't be installing a 3 year old (or older) add-on. Also, you need to be careful when using the Add-on Compatibility Reporter.

NoScript 2.2.6 is compatible beyond Firefox 9.0.1. As far as Kaspersky add-ons go, check with their support to see which versions of Firefox they currently support. Kaspersky has been the slowest of the big 5 security vendors at keeping their stuff up to date with Firefox.

Very helpful info...thank you. Is it possible that the HP Smart Web Printing add-on was transferred over to my new computer with other data? Can you tell me who the big 5 security vendors are? Also, can you elaborate on using care with the Compatibility Reporter...I was under the impression that it was a useful FF tool?

Sorry, I don't know how or why an outdated add-on would be installed on a new PC, probably related to installing the HP printer software on the new PC. I doubt if it was transferred with Firefox data files, as the HP SWP add-on isn't installed directly into Firefox - it's installed when the Firefox Profile is first run after the installation of the HP software and Firefox see's a "new add-on" in the registry, but would be rejected by Firefox due to lack of version number compatibility. My guess is that the entire Profile was copied to the new PC from an existing Firefox installation which already had that SWP add-on installed, and not only the Firefox data files.

Norton / Symantec
McAfee
Zone Alarm
Trend Micro
Kaspersky
based upon US sales - not quality

https://addons.mozilla.org/en-US/firefox/addon/add-on-compatibility-reporter/

Help Mozilla make sure your favorite add-ons get updated for upcoming Firefox releases by using this extension to report whether they still work or are having some issues with alpha and beta releases. Note: Recommended for alpha and beta users only!

The Add-on Compatibility Reporter is intended to enable technically incompatible (internal version number is too low for the version of Firefox being used on) add-ons so the user can see if the add-on is or isn't compatible, and then report the status back to Mozilla. It doesn't fix a broken or truly incompatible add-on, that is up to the developer of each add-on to do the fixin'. Yes, it is useful, when used as intended and not with the expectation of it being a "magic wand" or elixir. There's no "cure-all" for add-ons compatibility.
But this is going to change with Firefox 10, which will assume that add-ons made for Firefox 4.0 or higher are "compatible" with Firefox 10 and not disable those add-ons as currently being done due to "perceived incompatibility" based upon version numbers. On the surface it seems like a good idea, but once users start having problems with Firefox due to add-ons that previously would have been disabled (due to version number mismatch) - it's going to be up to each user to try to figure out which add-on is causing the problems - in much greater numbers than we are seeing now. I'm a pessimist by nature, so that's my prediction of what we might see with Firefox 10 and the "assumption that all add-ons are really compatible".