Could you check the MacOS Activity Monitor to see whether you can find Firefox running there:

https://support.apple.com/guide/activity-monitor/welcome/mac

While it's not ideal to "crash" Firefox by force quitting it, that might be required in some cases if a simple quite or restarting the system doesn't clear it out.

Thanks jscher 2000 for your reply. Yes, I looked for the bug on Activity Monitor. Others have written about this problem, and the solution has been to delete a 'profile lock' file. I think I deleted the wrong 'default ...' file, then tried to recover Firefox by installing another updated copy, so now I have three 'default' files and I have no idea which one or ones to delete. I do not want to lose my original bookmarks and configurations,

So I wait for some brilliant, kind techie to help me solve this.

To get an idea of which profile folder has the goods, click into their respective bookmarkbackups folders and see which one has the best history of bookmark backup files.

Note: these compressed files are not intended to be read by other programs, only Firefox's restore feature. However, I do have a converter on my site if needed: https://www.jeffersonscher.com/ffu/bookbackreader.html

Yes, thanks for that info, jscher 2000. I have a Firefox account through my business email. (I have another through my personal email, and that might be why I'm having this profile lock problem???)).

I'm fairly certain, Mozilla/Firefox have a record of my browser set-up, so I'm fairly confident I can return an updated version of the browser to my original set-up. However, I can't open any Firefox browser now because of the locked profile bug still preventing that. I don't want to have to do a clean uninstall. I have a backup copy of Firefox on a portable hard drive just waiting to be reinstalled, at which point, I'll just install the update which will integrate the original set-up onto the update. But first I have to get this profile lock bug problem figured out or any updates or reinstalls will run into the same error ... "a copy of Firefox is already open".

Okay, I'm not sure what you tried so far.

Can you open and view the files in individual profile folders in Finder? If not, this article has the method for getting to them when Firefox won't run (if it doesn't show Mac-specific instructions, use the OS selector on the right side to switch to Mac):

Profiles - Where Firefox stores your bookmarks, passwords and other user data

In each folder, can you find and remove a parent.lock file? Please do not remove any other files or folders at this point.

Thanks, jscher 2000, for all this info. I was able to locate the Profiles, and I have three profile folders: 1) 0kr25gzy.default-release 2) 8638osoq.default-1513387167461 3) k8u9jknd.default-release-1

I see no parent lock file in any of these folders. However, I only saw any bookmark backups in the 'bookmarkbackups' folder in the second profile folder: 8638osoq.default-1513387167461. So I'm assuming that is the profile linked to my older version of Firefox that I have backedup on a portable hard drive. So what happens if I delete the other two profile folders? And where is this parent lock file? I've just searched my Mac for this file and nothing comes up?? Others have said this file is what's preventing me from opening the browser and giving this 'another copy is already open' message. Others that have run into this problem discovered they had two profiles. One guy deleted one of them not knowing what would happen, and luckily, it was the correct profile he deleted. His system worked fine afterward. I did the same thing when I discovered I had two profiles, but I must have deleted the wrong one because it didn't solve the 'another copy is open' problem. Then I uploaded another install of Firefox and now have three profile folders. So that's why I think I should delete the 'default-release' and 'default-release-1' profiles. Then I'd uninstall the latest version of Firefox (that can't open), and reinstall the backup version (older version on my portable hard drive). What do you think? Also, I've been able to recover my business email account and have just setup a recovery key with Firefox so I can recover all my bookmarks, configs if I have to do a clean uninstall and reinstall. So I think we're getting there, thanks to you. But I'd love to hear your suggestions.

It would be better to avoid deleting the profile folder that Firefox has listed as your current default profile. That will cause a different error: How to run Firefox when your profile is missing or inaccessible.

Are you able to start Firefox up in the classic Profile Manager (this is a dialog that displays early in the launch process)? See the steps under "Start the Profile Manager when Firefox is closed" in the following article:

Profile Manager - Create, remove or switch Firefox profiles

Try to select the one with the long number and start Firefox in that profile and see whether it works.

Did you check the dates in each profile because 1513387167461 means that the profile got created in December 2017 due to a reset.

A dedicate profile like 0kr25gzy.default-release or k8u9jknd.default-release-1 would be more recent, the latter got possibly created due to issues with profiles.ini. The date-time of times.json file should give a clue when these profiles got created (its content has time strings in Unix Epoch similar to 1553029392075.

• https://www.epochconverter.com/

If you use the Time Machine or other backup then try to restore file(s) from this backup.

• https://www.apple.com/support/timemachine/

Firefox uses two locations for the Firefox profile folder, so make sure to look in the correct location. Location used for the main profile that keeps your personal data (Root Directory on about:profiles).

• ~/Library/Application Support/Firefox/Profiles/<profile>

Location used for the disk cache and other temporary files (Local Directory on about:profiles).

• ~/Library/Caches/Firefox/Profiles/<profile>

• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

This whole Firefox situation is so screwed up. First of all, I can locate the Profile folder only by using this Terminal instruction: /Applications/Firefox.app/Contents/MacOS/firefox-bin -P (thanks jscher 2000!). But I can not find any Firefox folder in Library/Application Support, either on my computer or on the backup portable hard drive files? Really weird. I can type in Spotlight 'profile' and do find the Profile folder listed, and it tells me it's located in Library/Application Support, but it's not there, so it's hidden or something? Weird.

I made a backup on the system in late December. A few days before I installed an updated version of Firefox, so that's what I backed up. I really can't remember all the things I've done since then, or if Firefox was working at the time of the backup or install of the update. I'm so lost, and my computer seems lost too.

I am now inclined to just delete all the profiles (at last count there's three of them), and uninstall all versions of Firefox on my computer and the backup. Then I'd do a clean reinstall. But can you tell me if I can recover my bookmarks, other apps and their configurations that were bookmarked to Firefox if I do this? I have a recovery key that I created and saved, and Firefox Account should have my setup saved in it which I can access after I install a new version. Sorry if this all kinda confusing.

Another question. This is the old Firefox profile that should containall my setup: 8638osoq.default-1513387167461. But, jscher 2000, you say 'use that profile to open Firefox'/ How do I do that?

OK. I was able to open Firefox using the times.json file. (Thanks cor-el) I have three of them, all linked to the three different profiles of Firefox. All three opened a brend new version of Firefox. Version 84.0.2 that was already installed on the computer (the latest version), and, then, after putting the latest version in the Trash, I copied the Firefox (version 84.0.1 on portable hd) back onto the computer, did the same with the times.json files. In all cases, I got a brand new version of Firefox without any of the old setup or configs. So apparently, when I installed the 84.0.1 version in late December, my original setup/profile somehow got lost and did not integrate with the 84.0.1 version. The 84.0.2 version certainly doesn't have any of this setup either.

(So I think I have my old profile somewhere in the computer hard drive, but I have no idea what to do with it. I'm pretty sure it's this file: 8638osoq.default-1513387167461, which epoch converter tells me was created on May 2 00:17:41 EDT 49927. What year is EDT 49927? The other two profiles: default-release, and default-release-1, are, I think, the 84.0.1 and 84.0.2 installs I did in the past few weeks. But I don't want to delete any of these profiles until I understand what I'm doing.

So it looks like I can at least open Firefox. Now, how do I restore it to the pre-December state with bookmarks, etc? Like I said, I did make a recovery key two days ago. Please help. Thanks so much!

In Mac OS X v10.7 and later, the "~/Library" folder in the Home directory is a hidden folder.

• https://www.macworld.co.uk/how-to/mac-software/hidden-files-mac-3520878/

Thanks again to cor-el and jscher2000 for your help.

I am now able to see the Library folder and access Application Support/Firefox, and the three profiles. (I had no idea Mac hid system folders). I checked out the oldest profile, the one with all my bookmarks. The other two profiles have no saved bookmarks. So I'm assuming this is my profile before I updated it in late December. So in this file, I've opened several of the .json folders, such as logins.json, addons.json, containers.json, extensions.json. All open files with the login info, extension info, etc. files and instructions. And all also trigger Firefox to open, but it's a brand new version of Firefox, but with no old configs and bookmarks.

Seems I'm getting close.

So how do I restore the Firefox with all the bookmarks and configs like it was in early December? Use the recovery key? Some magic Terminal instruction? Some file in the Application Support/Firefox/Profiles folder, or some other file or folder there? And after I do restore it, should I delete the other two profiles?

You can use the Profile Manager or the about:profiles page to select the profile with you bookmarks.

• https://support.mozilla.org/en-US/kb/recover-user-data-missing-after-firefox-update

Hey, cor-el and jscher 2000, you two have helped me solve the problem. Definitely couldn't have done it without you. I now know the inner workings of Firefox and Mac much better. I copied and pasted my old configs and setup from the old profile into the new 'default-release' Firefox browser, and all is working fine. So thanks again!!