The next time you see this, could you make a note of what script is not responding? Sometimes this points to an add-on as the source of the problem. Speaking of add-ons... Could you test in Firefox's Safe Mode? That's a standard diagnostic tool to deactivate extensions and some advanced features of Firefox. More info: [[Troubleshoot Firefox issues using Safe Mode]]. ''If Firefox is not running:'' Hold down the Shift key when starting Firefox. ''If Firefox is running:'' You can restart Firefox in Safe Mode using either: * "3-bar" menu button > "?" button > Restart with Add-ons Disabled * Help menu > Restart with Add-ons Disabled and OK the restart. ''Both scenarios:'' A small dialog should appear. Click "Start in Safe Mode" (''not'' Refresh). Does the issue still occur?