Let's make sure your system is clean.

You may have ad/mal-ware. Further information can be found in this article; https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware?cache=no

Run most or all of the listed malware scanners. Each works differently. If one program misses something, another may pick it up.

Thank you Fred for your help. I have run the Malware software and also I have Intego Virus protection and all have scanned negative. I still cannot open the Firefox app, other than through the Profile Manager. I note that Apple's protection system, System Integrity Protection, prevents certain applications reaching the root directory eg , user libraries and wondered if that could be related to Firefox not starting up?

Chris

Let’s do a full clean re-install;

Note: Firefox comes in three or more folders on all computers. They are;

Maintenance: (Programs Folder) <Windows Only> Firefox itself: (Programs Folder) And two folders in the profile of each user on the computer for each Firefox profile for that user.

If you remove the Firefox folder, the user profiles would not be affected.

Download Firefox For All languages And Systems {web link}

Save the file. Then Close Firefox.

Using your file browser, open the Programs Folder on your computer.

Windows: C:\Program Files C:\Program Files (x86) Note: Check Both Folders

Mac: Open the "Applications" folder. https://support.mozilla.org/en-US/kb/how-download-and-install-firefox-mac

Linux: Check your user manual. If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it. See Install Firefox on Linux; https://support.mozilla.org/en-US/kb/install-firefox-linux

If you downloaded and installed the binary package from the Firefox download page, simply remove the folder Firefox in your home directory. http://www.mozilla.org/firefox#desktop ++++++++++++++++++++++++++++ Look for, and remove any Mozilla or Firefox program folders. Do not remove the Mozilla Thunderbird folder if there is one.

Do Not remove any profile folders.

After rebooting the computer, run a registry scanner if you have one. Then run the installer. +++++++++++++++++++++++++++ If there is a problem, start your Computer in safe mode and try again.

http://encyclopedia2.thefreedictionary.com/Linux+Safe+Mode This shows how to Start all Computers in Safe Mode; Free Online Encyclopedia

If the above does not help:

Use these links to create a new profile. Use this new profile as is. Is the problem still there?

https://support.mozilla.org/en-US/kb/how-run-firefox-when-profile-missing-inaccessible

http://kb.mozillazine.org/Profile_folder_-_Firefox#Navigating_to_the_profile_folder

https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

Type about:profiles<enter> in the address bar.

Hi Fred thanks for your patience. I have undertaken all the tasks listed above.

ie, downloaded (again) Firefox 75, removed Firefox app from Applications folder, left one and only profile, looked for other Firefox.app programs, then re installed in normal and then safe mode. The same message comes up, a picture of which I have attached. I could only start up the app using the profile manager using the Terminal window. I tried using a new profile with no success. I have attached a picture of the file directory where the profile is kept.

I am sorry to be difficult

Chris

I called for more help.

Hi I think I may have found a solution. I had both the Firewall on for my Mac and Vault encryption. When I added Firefox to the Firewall settings and then turned off Vault Encryption I could open the program but with the following message. So now I can open Firefox from the Dock but the. app does not seem to be in the Applications Folder. A bit strange.

Hopefully it will work as I have synced my settings

Did it work?

If you have sync, and there is a problem anywhere, Shut Down Sync Immediately On All Devices to prevent the problem from spreading. Once the problem is fixed, perform the same repair on all computers/profiles before using sync again.

Yes it appears to have worked.

That was very good work. Well Done.