diff --git a/netwerk/protocol/http/UserAgentOverrides.jsm b/netwerk/protocol/http/UserAgentOverrides.jsm
index 404a9369065b..c900dab853e1 100644
--- a/netwerk/protocol/http/UserAgentOverrides.jsm
+++ b/netwerk/protocol/http/UserAgentOverrides.jsm
@@ -67,6 +67,7 @@ this.UserAgentOverrides = {
       // UA override might not work correctly.
     }
 
+    Services.obs.notifyObservers(null, "useragentoverrides-initialized");
     gInitialized = true;
   },