Firefox item is in the Startup folder

1. Click the Windows Start button.
2. Go to All programs.
3. From the programs list, select the Startup folder.
4. Search for Firefox or a document that causes Firefox to open in the list of startup items. If you found one, right-click it and select Delete. Confirm the deletion by clicking Yes.

Malware causing Firefox to load on startup

Sometimes, Malware (for example Viruses, Worms and Spyware) can cause Firefox to start together with Windows and probably display malicious sites. See Troubleshoot Firefox issues caused by malware for further details and troubleshooting steps.

Firefox item is in your account's Login Items

1. Open System Preferences.
2. Go to the Accounts panel.
3. Select the name of the user from the left-hand side.
4. Click the Login Items tab.
5. Search for Firefox in the list and select it.
6. Click the - button to delete Firefox from the list.

Firefox item is in your account's Startup Applications

(Ubuntu)

1. Open the System menu.
2. Go to the Preferences sub-menu and select Startup Applications.
3. Search for Firefox in the list and select it.
4. Click the Remove button to delete Firefox from the list.