From MozillaZine Knowledge Base
Users can choose to have their browser load a given page each time the browser starts. This preference keeps track of that URL.
Possible values and their effects
The URL to load when the browser starts and browser.startup.page is set to 1.
The field “Home Page” under “Tools → Options → Main → Startup” sets this preference.
The field “Home Page” under “Tools → Options → General → Startup” sets this preference.
First checked in
Has an effect in