Do you have the Firefox icon on your quick launch? Right click on it, and select Open New Window. Sometimes this works. If it opens, close it by Menu > File > Exit.

This is not a cure but will make it easier if Firefox locks up in Windows. https://support.mozilla.org/questions/997866 {web link}

The above method did not work.

Did you try the link I posted?

Sometimes when FF is closing, not all of it shuts down properly. On Windows, start the Task Manager. (Other systems may have different names and / or commands). Select Processes. Look down the list for Firefox. Right click and select End Task.

Once you have closed Firefox,

Start Firefox in Safe Mode {web Link} by holding down the <Shift>
(Mac Options) key, and then starting Firefox.

While still in Safe Mode,

Type about:support in the address bar and press Enter. Under the main banner, press the button; Copy Text To Clipboard.. Then in the reply box at the bottom of this page, do a right click in the box and select Paste. This will show us your system details. No Personal Information Is Collected.

After the above, close Firefox. Any problem?

Try to remove the parent.lock file in the Firefox profile folder.

• C:\Users\<user>\AppData\Roaming\Mozilla\Firefox\Profiles\<profile>\
• http://kb.mozillazine.org/Profile_folder_-_Firefox

See:

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

What security software do you have?

Try to create a new Firefox desktop shortcut and possibly reinstall Firefox via a clean reinstall (i.e. delete the Firefox program folder).

If you can't delete the Firefox program folder then try to rename this folder to "Mozilla Firefox.old".

• (64 bit Windows) "C:\Program Files (x86)\Mozilla Firefox\"
• (32 bit Windows) "C:\Program Files\Mozilla Firefox\"

Boot the computer in Windows Safe Mode with network support (press F8 on the boot screen) to see if that helps.

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/
• http://www.7tutorials.com/4-ways-boot-safe-mode-windows-10

FredMcD said

Did you try the link I posted?

---

Sometimes when FF is closing, not all of it shuts down properly. On Windows, start the Task Manager. (Other systems may have different names and / or commands). Select Processes. Look down the list for Firefox. Right click and select End Task.

I did try the link that you posted, and it did not work. FF is not listed in the "Processes" tab in Task manager, as I mentioned it is only listed on the "Details" tab.

FredMcD said

Once you have closed Firefox, Start Firefox in Safe Mode {web Link} by holding down the <Shift>
(Mac Options) key, and then starting Firefox. While still in Safe Mode, Type about:support in the address bar and press Enter. Under the main banner, press the button; Copy Text To Clipboard.. Then in the reply box at the bottom of this page, do a right click in the box and select Paste. This will show us your system details. No Personal Information Is Collected.

---

After the above, close Firefox. Any problem?

FF will not start in safe mode, because it will not start.

cor-el said

Try to remove the parent.lock file in the Firefox profile folder.

• C:\Users\<user>\AppData\Roaming\Mozilla\Firefox\Profiles\<profile>\
• http://kb.mozillazine.org/Profile_folder_-_Firefox

See:

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

What security software do you have?

---

Try to create a new Firefox desktop shortcut and possibly reinstall Firefox via a clean reinstall (i.e. delete the Firefox program folder).

If you can't delete the Firefox program folder then try to rename this folder to "Mozilla Firefox.old".

• (64 bit Windows) "C:\Program Files (x86)\Mozilla Firefox\"
• (32 bit Windows) "C:\Program Files\Mozilla Firefox\"

Boot the computer in Windows Safe Mode with network support (press F8 on the boot screen) to see if that helps.

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/
• http://www.7tutorials.com/4-ways-boot-safe-mode-windows-10

I've tried a clean install, but I cannot delete the FF program folder, even if I change it to "Mozilla Firefox.old." I'll try booting in safe mode and get back to you.

And we're up and running again. Booted in safe mode and was able to delete the FF folder. Once I restarted, I did a new install of FF and everything is working fine. Thank you for your help.

Hello,

I am glad to hear that your problem has been resolved. If you haven't already, please select the answer that solves the problem. This will help other users with similar problems find the solution more easily.

Thank you for contacting Mozilla Support.

jimmyjkjr said

cor-el said

<snip> reinstall Firefox via a clean reinstall (i.e. delete the Firefox program folder). If you can't delete the Firefox program folder then try to rename this folder to "Mozilla Firefox.old".

• (64 bit Windows) "C:\Program Files (x86)\Mozilla Firefox\"
• (32 bit Windows) "C:\Program Files\Mozilla Firefox\"

Boot the computer in Windows Safe Mode with network support (press F8 on the boot screen) to see if that helps.

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/
• http://www.7tutorials.com/4-ways-boot-safe-mode-windows-10

I've tried a clean install, but I cannot delete the FF program folder, even if I change it to "Mozilla Firefox.old." I'll try booting in safe mode and get back to you.

jimmyjkjr said

And we're up and running again. Booted in safe mode and was able to delete the FF folder. Once I restarted, I did a new install of FF and everything is working fine. Thank you for your help.

Thanks for posting the outcome. I'll mark cor-el's answer as the solution.