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

If you abort a profile refresh then this can cause your profile to get lost because Firefox might be holding the profile folder in memory in order to move it to the "Old Firefox Data" folder on the desktop. If you interrupt this process then you might lose all your data. If you use the Time Machine or other backup then try to restore this profile from this backup. *http://www.apple.com/support/timemachine/ Can you use the Profile Manager to create a new profile? *https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles You can check if you have an orphaned profile that may not show in the Firefox Profile Manager. *~/Library/Application Support/Firefox/Profiles/<profile>/ The ~/Library folder where Firefox creates its profiles is a hidden folder. *http://kb.mozillazine.org/Show_hidden_files_and_folders If you have found an orphaned profile then you may want to recover some personal data or restore his profile. *https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile See also "Profile was moved or renamed": *https://support.mozilla.org/en-US/kb/how-run-firefox-when-profile-missing-inaccessible Note that you should never use "Choose Folder" to specify a folder that already contains files that do not belong to Firefox. Only use "Choose Folder" to recover an profile that isn't listed in the Profile Manager.