diff --git a/browser/components/nsBrowserGlue.js b/browser/components/nsBrowserGlue.js
index a9d95bb0cf..f25c6c0d67 100644
--- a/browser/components/nsBrowserGlue.js
+++ b/browser/components/nsBrowserGlue.js
@@ -406,7 +406,7 @@ BrowserGlue.prototype = {
     os.addObserver(this, "flash-plugin-hang", false);
     os.addObserver(this, "xpi-signature-changed", false);
     os.addObserver(this, "autocomplete-did-enter-text", false);
-    Services.prefs.addObserver(PREF_INTERNAL_USERSCRIPTS_ENABLED, this);
+    Services.prefs.addObserver(PREF_INTERNAL_USERSCRIPTS_ENABLED, this, false);
 
     if (AppConstants.NIGHTLY_BUILD) {
       os.addObserver(this, AddonWatcher.TOPIC_SLOW_ADDON_DETECTED, false);
diff --git a/toolkit/modules/addons/MatchPattern.jsm b/toolkit/modules/addons/MatchPattern.jsm
index 8c09a509e6..e46102b75d 100644
--- a/toolkit/modules/addons/MatchPattern.jsm
+++ b/toolkit/modules/addons/MatchPattern.jsm
@@ -89,9 +89,22 @@ SingleMatchPattern.prototype = {
       let suffix = host.substr(2);
       let dotSuffix = "." + suffix;
 
-      return ({host}) => host === suffix || host.endsWith(dotSuffix);
+      return uri => {
+        try {
+          let host = uri.host;
+          return host === suffix || host.endsWith(dotSuffix);
+        } catch (e) {
+          return false;
+        }
+      };
     }
-    return uri => uri.host === host;
+    return uri => {
+      try {
+        return uri.host === host;
+      } catch (e) {
+        return false;
+      }
+    };
   },
 
   matches(uri, ignorePath = false) {