What's your computer system and Firefox version?

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

I'm using macOS Mojave 10.14 and trying to install the latest version of Firefox.

I can't use the Profile manager, when trying to start it it gives me the same error as when trying to start firefox.

Did you check out the links I posted?

Yes. Both of the directories where the profiles folder could be located are empty. And I can't start Profile manager

You may have a corrupt profiles.ini file. Close Firefox. Open your file browser to this hidden location:

• Mac: *~/Library/Application Support/Firefox/
• Linux: *~/.mozilla/firefox/
• Windows: %AppData%\Mozilla\Firefox\
• *C:\Users\<user>\AppData\Roaming\Mozilla\Firefox\

Locate the profiles.ini file. Then rename or delete it.

Restart Firefox. Use this new profile as is. Is the problem still there?

I've already removed that file

Firefox should have noticed and created a new profile.

Let’s do a full clean re-install;

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

I've already tried to reinstall. I tried again just to be sure and it didn't work.

I called for more help.

Did you try to remove the Firefox folder in both locations and also check for write permission issues?

Location used for the main profile that keeps your personal data in "AppData\Roaming" (Root Directory on about:profiles).

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

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

• ~/Library/Caches/Firefox/Profiles/

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

• http://kb.mozillazine.org/Show_hidden_files_and_folders#Mac_OS_X

Yes, I've removed both profiles directories, even the Firefox ones, and then tried to reinstall.

I've managed to solve it!! When i tried to download a playlist from Spotify and gave me an error saying that maybe my hard drive was full, even though I had a lot of space left, i suspected that it might not be a problem with Firefox but my system. Apparently it was a writing permission as someone mentioned.

I just entered the command $ diskutil resetUserPermissions / `id -u` as this article explained.

Thanks for the help!

That was very good work. Well done.