--- a/netwerk/protocol/http/UserAgentOverrides.jsm
+++ b/netwerk/protocol/http/UserAgentOverrides.jsm
@@ -62,16 +62,17 @@ this.UserAgentOverrides = {
       });
 
       buildOverrides();
     } catch (e) {
       // UserAgentOverrides is initialized before profile is ready.
       // UA override might not work correctly.
     }
 
+    Services.obs.notifyObservers(null, "useragentoverrides-initialized");
     gInitialized = true;
   },
 
   addComplexOverride: function uao_addComplexOverride(callback) {
     // Add to front of array so complex overrides have precedence
     gOverrideFunctions.unshift(callback);
   },