Hello optics, This link help you a lot '''How to download and install firefox in macos with easy steps ''' http://mzl.la/1xKrRru

I still get a "missing profile" error message.

Hi optics, You need to locate the profiles.ini file and delete this file or use the Profile Manager to create a new profile. See: https://support.mozilla.org/kb/how-run-firefox-when-profile-missing-inaccessible This issue can be caused by a problem with the profiles.ini file or with the permissions (owner) of involved folders. You can use one of these to make Firefox create a new default profile or recover an existing profile: * Delete the profiles.ini file to make Firefox create a new (default) profile * Use the Profile Manager to create a new profile * If you still have an existing profile then click "Choose Folder" in the Profile Manager and browse to the location of a lost profile to recover this profile * https://support.mozilla.org/kb/Managing+profiles You should find the profiles.ini file in this hidden location: * Windows: %AppData%\Mozilla\Firefox\ * *C:\Users\<user>\AppData\Roaming\Mozilla\Firefox\ * Mac: ~/Library/Application Support/Firefox/ * Linux: ~/.mozilla/firefox/ If clearing the profiles.ini file isn't working then also check the location of the cache files. * Windows: *C:\Users\<user>\AppData\Local\Mozilla\Firefox\Profiles\<profile>\ * Mac: ~/Library/Caches/Firefox/Profiles/ * Linux:~/.cache/mozilla/firefox/ You can also try to rename/delete the MozillaFirefox folder in both above mentioned locations (main, cache). http://kb.mozillazine.org/Profile_Manager https://support.mozilla.org/kb/Managing+profiles http://kb.mozillazine.org/Profile_folder_-_Firefox Hope it helps. Thank You.