Hello,

You may have seen a post or received a notification regarding support for Firefox or Thunderbird with a link to another site or a phone number being posted. This is a scam and is not a method to receive support from Mozilla. Mozilla does not have telephone or email support. Please do not click on the link and do not interact by calling any phone numbers or email addresses listed. I apologize for any inconvenience caused. You are currently posting on the official Mozilla website and will receive assistance here.

https://support.mozilla.org/kb/Firefox+is+already+running+but+is+not+responding

https://www.basezap.com/cant-open-firefox-because-a-copy-of-firefox-is-already-open-mac/

https://apple.stackexchange.com/questions/196771/cant-open-firefox-because-a-copy-of-firefox-is-already-open

http://kb.mozillazine.org/Firefox.exe_always_open

+++++++++++++++++++++++++++++++++++++++++

https://support.mozilla.org/en-US/kb/firefox-slow-how-make-it-faster

https://support.mozilla.org/en-US/kb/firefox-uses-too-many-cpu-resources-how-fix

https://support.mozilla.org/en-US/kb/firefox-uses-too-much-memory-ram

https://support.mozilla.org/en-US/kb/firefox-hangs-or-not-responding

https://support.mozilla.org/en-US/kb/firefox-takes-long-time-start-up

https://support.mozilla.org/en-US/kb/quick-fixes-if-your-firefox-slows-down

I deleted the (hidden file) lockparent, but this did not solve the problem. I still can't figure out if Firefox, by freezing, is freezing my Mac, or if the Mac itself is at fault. But after I have to Force Quit Firefox, I can't do a normal shut down. The icons and cursor disappears, but the screen stays on with my wallpaper photo. I have to press the power button to turn the Mac off. I suspect Firefox is still somehow active, even if not in the Force Quit box any more and not in Terminal.

Hello glands666,

Sometimes Refreshing the browser can fix many problems.

Try Refreshing the browser:-

• To do this, click the menu button at the top right corner of the Firefox window.

• Click the “Help” option near the bottom of the menu.

• Click the “Troubleshooting Information” option in the Help menu.

• Click the “Refresh Firefox” button at the top right corner of the Troubleshooting Information page.

• You’ll be warned that this will remove your browser add-ons, reset your customizations, and revert other browser data to the default settings. Click “Refresh Firefox” to confirm you want to make these changes.

If it doesn't solved your problem, then feel free to ask in Reply Section. Thanks for raising your question in Mozilla Support Forum.

Thank you for your thoughts. I did refresh Firefox, but by the end of the day, both my home iMac and my office iMac were back freezing. It always seems to happen when several windows are open. I still have AdBlock installed at the office, but I don't see it as installed anymore at home.