This happens in safe mode?

• Firefox in safe mode

Also:

• Reset Firefox
• Create a new profile

Tabs in safe mode work. Does this mean I have a dysfunctional add-on? If so, how do I figure out which one? Thanks for the quick response.

SImple look to this article:

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

the obvious candidate would be tab-mix-plus, since it alters the behaviour of tabs. there is a new version of it available, so try updating it...

Diego and Philipp,

It was the add-on microsoft.net, which is not compatible with firefox 29. I have not yet re-enabled tab-plus, but will try it and see what happens. Thanks again for the help.