From MozillaZine Knowledge Base
In order to make sure users see the end-user license agreement when the EULA changes, Mozilla keeps track of which EULAs have been accepted. This preference allows the EULA check to be disabled.
Possible values and their effects
Never display the EULA to the user for their agreement. (Default in debug builds)
Display the EULA to the user if havenâ€™t agreed to the current version.
First checked in
Has an effect in