Backed out 3 changesets (bug 1325464) for xpcshell failures a=backout

Backed out changeset 562ddc32cc21 (bug 1325464)
Backed out changeset cd10db6087dd (bug 1325464)
Backed out changeset 4079437c4648 (bug 1325464)

toolkit/components/privatebrowsing/PrivateBrowsingTrackingProtectionWhitelist.js

@@ -58,7 +58,7 @@ PrivateBrowsingTrackingProtectionWhitelist.prototype = {
     return this._allowlist.indexOf(uri.spec) !== -1;
   },
 
-  observe(subject, topic, data) {
+  observe: function(subject, topic, data) {
     if (topic == "last-pb-context-exited") {
       this._allowlist = [];
     }