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

• Don't make any changes on the Safe mode start window.

See:

• Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems

If it does work in Safe-mode then disable all extensions and then try to find which is causing it by enabling one at a time until the problem reappears.

• Use "Disable all add-ons" on the Safe mode start window to disable all extensions.
• Close and restart Firefox after each change via "File > Exit" (Mac: "Firefox > Quit"; Linux: "File > Quit")

cor-el, thank you very kindly! It worked!

You're welcome.

Can you tell us which extension caused your problem?
It help others who read this thread.

I am not sure. I just went ahead and enabled Adobe, Flash, Java, Google Map, Picassa, Windows Media Player, and Microsoft Office Live.

I did ''not'' enable Silverlight, Shockwave for Director, Java Deployment Toolkit, I-Tunes Application Detection, Hulu Desktop

That are plugins (Tools > Add-ons > Plugins).

An extension is a more likely cause of your problem.

Did you disable or uninstall any extensions (Tools > Add-ons > Extensions)?

The Ask Toolbar extension, which ThomasCSS has installed, is known to cause that problem with being able to open new Tabs.