From MozillaZine Knowledge Base
Firefox 2.0 incorporates the Google Safe Browsing extension in its own Phishing Protection feature to detect and warn users of phishy web sites. This preference specifies which Safe Browsing provider to use.
Possible values and their effects
A non-negative integer indicating which Safe Browsing provider to use. (Default is 0)
Corresponds to a dropdown of Safe Browsing service provider(s), located under “Tools → Options → Security / Tell me...”
First checked in
Has an effect in