• Control-click on the Firefox Dock icon and uncheck 'Open at Login'
• Click Accounts (in the System row of the System Preferences window)
  • Click the Login Items tab
  • Click on Firefox in the list
  • Click the Minus (-) button

• https://support.mozilla.org/kb/Firefox+launches+automatically+when+your+computer+starts
• http://www.apple.com/findouthow/mac/#tutorial=startup - Open Applications Automatically on Startup

I am familar with those. That is what I meant when I said I have verified that my Preferences Login items does not include Firefox. The solution ios not to be found in either of those steps.

I have checked the ~/Library/LaunchAgents foilder and I do not think that any of the 3 files contained therein would cause Firefox to launch; ws.agile.1PasswordAgent.plist, com.google.keystone.agent.plist, com.apple.CSConfigDotMacCert-XXXXXXX-SharedServices.Agent.plist.

I have checked for mozilla files in places that might cause Firefox to launch but have not found any that I think could be the cause.

Did you check the first item?

• Control-click on the Firefox Dock icon and uncheck 'Open at Login'

I checked that the first time I had problems. It was not checked and I have subsequently checked and unchecked it to make sure.

I spent considerable time Friday and this morning troubleshooting the problem including completely removing Firefox and all associated files; then reinstalling Firefox and adding add-ons one by one. I have found the source of the problem.

I had Bitdefender for Macintosh installed. It has an anti-phishing module. The anti-phishing module installed in Firefox caused it to launch whenever I rebooted because Bitdefender was launched as part of the boot process. If I merely removed the anti-phishing module from Firefox, Firefox would launch wanted me to OK the addition of the anti-phishing module. Once I deleted Bitdefender, Firefox did not launch upon Startup. Why this does not happen with Safari, I do not understand. I will report the problem to Bitdefender technical support.