Do you have that problem when running in the Firefox SafeMode?
http://support.mozilla.com/en-US/kb/Safe+Mode
Don't select anything right now, just use "Continue in SafeMode."

If not, see this:
http://support.mozilla.com/en-US/kb/troubleshooting+extensions+and+theme...

Does not occur in safe mode, all working normally

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")

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

It appears to be the Real Player browser plugin version 14.01.1 that is causing the problem. Working normally now. Thanks for your help, appreciate it.

I had this same problem for some time now. In another Mozilla Firefox forum page related to this search one user said to disable the add on "Invisible Hand". I did that and rebooted and have multiple pages open now with multiple tabs and I could shut down the first tab on all the open windows. I think the "Invisible Hand" add-on s the culprit, at least in my case.