Not related to your question, but your plugins list shows outdated plugin(s) with known security and stability risks.

• Shockwave Flash 10.0 r42

Update the Flash plugin to the latest version.

• http://www.adobe.com/software/flash/about/

Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of your add-ons is causing your problem (switch to the DEFAULT theme: Tools > Add-ons > Themes).

See Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems and Troubleshoot issues with plugins like Flash or Java to fix common Firefox problems

I had this problem after I turned computer off due to lock up, reinstalling Firefox did nothing. My weird accidental fix, I installed Orca browser which is somewhat similarly engineered to Firefox, next time I opened Firefox it worked.

I had this start happening to me when the 'Ask toolbar' was installed.

I removed the toolbar, and uninstalled it completely. This then fixed the problem.

Try uninstalling any unwanted toolbars. This was definitely the cause of firefox not tabbing for me. Now Ctrl+T and the button works again.

Hope that helps.

Yes, Ask toolbar was the culprit. Uninstalled it and the new tab works now. Thank you chrishamps!!

Confirming that this worked perfectly (Feb 2011)

Remove ASK TOOLBAR. It is the main culprit. And best advice avoid installing any such tool bars as they are of no good/use. To remove Click on Tools Click on Ad-ons and then delete the ASK TOOLBAR from there. After this action you may be asked to restart so do so and you will be perfectly fine.

Happy Surfing...

Agreed with everyone else, it was the ASK Toolbar! I didn't even know I installed it I'm sure it was bundled w/ something else I hate that !

I have this problem, but as far as I can tell it has nothing to do with the "Ask" toolbar (which, according to my Add-ons list, I don't even have on my system). Instead, when I updated Firefox and Adobe, it asked me if I wanted to install the Google Chrome toolbar. I said no, and proceeded with the installation. Yet I'm still having the same problem as everyone else on this page--I can't open new tabs on a completely separate page anymore. Very annoying!

Yes, removing the Ask toolbar does the trick! You do it by bringing up Control Panel and clicking Programs & Features, then uninstall the Ask toolbar. THANKS!