--- a/toolkit/components/url-classifier/SafeBrowsing.jsm
+++ b/toolkit/components/url-classifier/SafeBrowsing.jsm
@@ -65,16 +65,17 @@ this.SafeBrowsing = {
     if (this.initialized) {
       log("Already initialized");
       return;
     }
 
     Services.prefs.addObserver("browser.safebrowsing", this, false);
     Services.prefs.addObserver("privacy.trackingprotection", this, false);
     Services.prefs.addObserver("urlclassifier", this, false);
+    Services.prefs.addObserver("plugins.flashBlock.enabled", this, false);
 
     this.readPrefs();
     this.addMozEntries();
 
     this.controlUpdateChecking();
     this.initialized = true;
 
     log("init() finished");