I would try reinstalling FireFox and make sure you aren't using a portable version.

Make sure Firefox gets installed properly. Open the Firefox Disk Image file and drag the Firefox application to the Applications folder on your hard drive. You shouldn't double-click the Firefox application to run it from the Disk Image, but instead drag it out of the DMG folder. <hr> *https://support.mozilla.org/en-US/kb/install-firefox-mac You can create a new profile to test if your current profile is causing the problem. See "Creating a profile": *https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles *http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over problems. *https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

Look on your desktop. Do you see a folder called; '''Old Firefox?''' Look inside. Look for the folder with the latest creation date. https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles https://support.mozilla.org/en-US/kb/how-run-firefox-when-profile-missing-inaccessible ----------------- 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. How many profiles are listed? How many should be there? Also, open the folder in your file explorer. ------------------ https://support.mozilla.org/en-US/kb/how-to-fix-preferences-wont-save '''Note:''' Some software, '''like''' Advanced SystemCare with Surfing Protection, can protect files in the Firefox profile folder against changes. If you have such software then check the settings or uninstall this software.