If you leave Firefox open when Windows shuts down, Firefox may automatically re-open with your previously opened tabs the next time you start Windows. Here's how to disable the feature.
Prevent Firefox from starting automatically
- Type about:config in the address bar and press EnterReturn.
A warning page may appear. Click to go to the about:config page.
- Search for toolkit.winRegisterApplicationRestart.
- Click the Toggle button next to it, to set its value to false.
There's no need to restart Firefox; the changes take effect immediately.