Bug 945828 - Work around bug 945756. r=luke

toolkit/components/jsdownloads/test/unit/test_DownloadList.js

@@ -362,9 +362,8 @@ add_task(function test_history_expiration()
   yield list.add(downloadTwo);
 
   // Force a history expiration.
-  let expire = Cc["@mozilla.org/places/expiration;1"]
+  Cc["@mozilla.org/places/expiration;1"]
-                 .getService(Ci.nsIObserver);
+    .getService(Ci.nsIObserver).observe(null, "places-debug-start-expiration", -1);
-  expire.observe(null, "places-debug-start-expiration", -1);
 
   // Wait for both downloads to be removed.
   yield deferred.promise;