Make sure that this also does not happen in Safe Mode:

Try Firefox Safe Mode to see if the problem goes away. Firefox Safe Mode is a troubleshooting mode that temporarily turns off hardware acceleration, resets some settings, and disables add-ons (extensions and themes).

If Firefox is open, you can restart in Firefox Safe Mode from the Help menu:

• Click the menu button , click Help and select Restart with Add-ons Disabled.

If Firefox is not running, you can start Firefox in Safe Mode as follows:

• On Windows: Hold the Shift key when you open the Firefox desktop or Start menu shortcut.
• On Mac: Hold the option key while starting Firefox.
• On Linux: Quit Firefox, go to your Terminal and run firefox -safe-mode
  (you may need to specify the Firefox installation path e.g. /usr/lib/firefox)

When the Firefox Safe Mode window appears, select "Start in Safe Mode".

If the issue is not present in Firefox Safe Mode, your problem is probably caused by an extension, theme, or hardware acceleration. Please follow the steps in the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article to find the cause.

To exit Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.

When you figure out what's causing your issues, please let us know. It might help others with the same problem.

Thanks. Did it but still had the same problem. Tabs do not respond with mouse over, will not select, will not close.

You seem to have a user.js file in your Profile folder. That is an optional file which is either user created or was created by an add-on that you have installed, to "lock" specific preferences.

Help > Troubleshooting information --> under Application Basics - Profile Folder -- click Show Folder

Then open that user.js in a text program like Notepad to see the contents of that file. If you don't understand what the contents of that user.js file are for, post the contents here.

I seen it happen where certain prefs in a user.js file weren't disabled in the Firefox SafeMode.

How did you know that? Contents of file: user_pref("capability.policy.policynames", "allowclipboard"); user_pref("capability.policy.allowclipboard.sites", "www.blogger.com us.f527.mail.yahoo.com mail.google.com pages.google.com"); user_pref("capability.policy.allowclipboard.Clipboard.cutcopy", "allAccess"); user_pref("capability.policy.allowclipboard.Clipboard.paste", "allAccess");

Bulbman, on the right side of this webpage there is a link to "More System Details", at the bottom of the pop up that will come up there is "User JS Yes". This is part of the troubleshooting information that is added when you create a question. :-)

Thanks. Now I know how you knew I had a js file. I copied and posted the file. Was there anything in the file that causes the issue?

The issue persists -- cannot select or close tabs in yahoo premium mail. The latest Firefox update has been installed. I reported the issue here because the functions work in Chrome (sorry).

us.f527.mail.yahoo.com sounds like it might be the website where you are having that problem.

Regardless, those prefs (capability.policy.allowclipboard.Clipboard...) are outdated and were removed from Firefox quite a few versions ago. Just delete that file and see if that solves your problem with Yahoo mail.

Thanks. The site with issues is https://us-mg6.mail.yahoo.com/neo/launch? but I thought the one you cite would be the problem too.

Deleted the file, restarted Firefox, problem persists.

Funny thing, if I get the pointer in just the right spot I can now select and close. Thanks for your help.