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
Only proceed if you are comfortable with advanced settings and understand the potential impacts.
- 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.