You can try to disable e10s in case you have enabled it. *browser.tabs.remote.autostart = false You can check for problems with the sessionstore.js and sessionstore.bak files in the Firefox profile folder that store session data. *Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder) *http://kb.mozillazine.org/Profile_folder_-_Firefox *http://kb.mozillazine.org/Multiple_profile_files_created ---- Create a new profile as a test to check if your current profile is causing the problem. See "Creating a profile": *https://support.mozilla.org/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. *http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

I don't have e10s enabled. I don't know where browser.tabs.remote.autostart is to change it. Making a new profile didn't work, it was still blank after copying the files across.

Firefox now opens 7 instances of itself when executed :(