Startup.homepage override url
From MozillaZine Knowledge Base
When a user starts up their browser after upgrading (i.e., if browser.startup.homepage_override.mstone is different than the last time the browser started), the URL specified in this preference is loaded instead of their homepage.
Possible values and their effects
The URL to use as a homepage when the browser starts after an upgrade. In Firefox, the default value is http://%LOCALE%.www.mozilla.com/%LOCALE%/%APP%/%VERSION%/whatsnew/, where %LOCALE%, %APP%, and %VERSION% are replaced with the value of general.useragent.locale, “firefox”, and the current browser version, respectively.
First checked in
Has an effect in