Hello,

We've received reports of users with the similar issue. This is likely caused by an add-on. Please try safe mode below and report back to us once you believe you know the culprit add-on causing the issue so Mozilla can contact the developer to release a fix.

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

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

• In Firefox 29.0 and above, click the menu button , click Help and select Restart with Add-ons Disabled.
• In previous Firefox versions, click on the Firefox button at the top left of the Firefox window and click on Help (or click on Help in the Menu bar, if you don't have a Firefox button) then click on 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, and you need to figure out which one. Please follow 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.

Thanks!

I'm not sure this related to addons. I only have basic -some would consider essential- extensions/addons.

When I have this problem Firefox also stops responding to other clicks eg you cant use the menu to look at addons, and doesn't respond to 'view passwords' or other options (Menu items dont respond).

However once having clicked Menu (with no result) I can then open another Tab. I have to repeat this until I have finished with all my work and various open tabs; then I can close Firefox and start afresh.

I have noticed that in this case having closed Firefox I cant reopen it because it just reports as "already running". I then have to open Task Manager and force Firefox task to close. What's going on?

It appears to be intermittent so I cant reproduce it at will, and running in 'safe' mode may or may not reveal it - hasn't yet.