Bug 1533763 - Enable setting the default referrer policy for third-party tracking resources to strict-origin-when-cross-origin when Enhanced Tracking Protection is turned on in Nightly; r=baku

Differential Revision: https://phabricator.services.mozilla.com/D24099

--HG--
extra : moz-landing-system : lando

modules/libpref/init/all.js

@@ -1765,7 +1765,12 @@ pref("network.http.referer.defaultPolicy", 3);
 // default cookie policy is set to reject third-party trackers;
 // to be used unless overriden by the site;
 // values are identical to defaultPolicy above
+#ifdef NIGHTLY_BUILD
+// On Nightly, trim referrers from trackers to origins.
+pref("network.http.referer.defaultPolicy.trackers", 2);
+#else
 pref("network.http.referer.defaultPolicy.trackers", 3);
+#endif
 // Set the Private Browsing Default Referrer Policy;
 // to be used unless overriden by the site;
 // values are identical to defaultPolicy above
@@ -1775,6 +1780,8 @@ pref("network.http.referer.defaultPolicy.pbmode", 2);
 // trackers;
 // to be used unless overriden by the site;
 // values are identical to defaultPolicy above
+// No need to change this pref for Nightly only since in private windows we
+// already trim all referrers to origin only.
 pref("network.http.referer.defaultPolicy.trackers.pbmode", 2);
 // false=real referer, true=spoof referer (use target URI as referer)
 pref("network.http.referer.spoofSource", false);