Several Mac users have reported this in the past 24 hours, and it appears to be caused by one or more extensions. Be especially suspicious of any that have "Community Toolbar" in the name.

Try disabling ALL nonessential or unrecognized extensions on the Add-ons page. Either:

• Ctrl+Shift+a
• "3-bar" menu button (or Tools menu) > Add-ons

In the left column, click Extensions. Then, if in doubt, disable. (Or if obviously unwanted, Remove)

Usually a link will appear above at least one disabled extension to restart Firefox. You can complete your work on the tab and click one of the links as the last step.

Does that restore normal new tab operation?

Thanks jscher2000, that worked a treat! Just need to work out which Add-on caused the issue!

If you could "name names" when you find out, that would be great.

Hmmm, have reloaded them all and can still get multiple tabs! :)

A weird but happy result. If the problem returns, let us know.

See also:

• http://kb.mozillazine.org/Prevent_websites_from_disabling_new_window_features