From MozillaZine Knowledge Base
Some information about the userâ€™s interaction with the Safe Browsing feature (if the user encountered a phishy page, what they did when the warning popped up, etc.) is collected and then reported back to the URL in this preference if this Safe Browsing service is selected in browser.safebrowsing.dataProvider.
Possible values and their effects
The URL to which report data is sent.
By default, the following preference and value exists:
In trunk builds:
First checked in
Has an effect in