diff --git a/platform/chromium/manifest.json b/platform/chromium/manifest.json
index f2570cbfb..2f924ab9b 100644
--- a/platform/chromium/manifest.json
+++ b/platform/chromium/manifest.json
@@ -2,7 +2,7 @@
     "manifest_version": 2,
 
     "name": "uBlock Origin",
-    "version": "1.3.1",
+    "version": "1.3.2",
 
     "default_locale": "en",
     "description": "__MSG_extShortDesc__",
diff --git a/platform/firefox/vapi-background.js b/platform/firefox/vapi-background.js
index a91ecae40..5df6011a5 100644
--- a/platform/firefox/vapi-background.js
+++ b/platform/firefox/vapi-background.js
@@ -1213,29 +1213,30 @@ var tabWatcher = (function() {
         }
     };
 
-    // https://developer.mozilla.org/en-US/docs/Mozilla/Tech/XPCOM/Reference/Interface/nsIWindowWatcher
-    var windowWatcher = {
-        observe: function(aSubject, topic) {
-            // https://developer.mozilla.org/en-US/docs/Mozilla/Tech/XPCOM/Reference/Interface/nsIWindowWatcher#registerNotification%28%29
-            //   "aSubject - the window being opened or closed, sent as an
-            //   "nsISupports which can be ... QueryInterfaced to an
-            //   "nsIDOMWindow."
+    // https://developer.mozilla.org/en-US/docs/Mozilla/Tech/XPCOM/Reference/Interface/nsIWindowMediator
+    // https://github.com/gorhill/uMatrix/issues/357
+    // Use nsIWindowMediator for being notified of opened/closed windows.
+    var windowListener = {
+        onOpenWindow: function(aWindow) {
             var win;
             try {
-                win = aSubject.QueryInterface(Ci.nsIInterfaceRequestor)
-                              .getInterface(Ci.nsIDOMWindow);
+                win = aWindow.QueryInterface(Ci.nsIInterfaceRequestor)
+                             .getInterface(Ci.nsIDOMWindow);
             } catch (ex) {
             }
-            if ( !win ) {
-                return;
-            }
-            if ( topic === 'domwindowopened' ) {
+            if ( win ) {
                 onWindowLoad(win);
-                return;
             }
-            if ( topic === 'domwindowclosed' ) {
+        },
+        onCloseWindow: function(aWindow) {
+            var win;
+            try {
+                win = aWindow.QueryInterface(Ci.nsIInterfaceRequestor)
+                             .getInterface(Ci.nsIDOMWindow);
+            } catch (ex) {
+            }
+            if ( win ) {
                 onWindowUnload(win);
-                return;
             }
         }
     };
@@ -1261,11 +1262,11 @@ var tabWatcher = (function() {
             }
         }
 
-        Services.ww.registerNotification(windowWatcher);
+        Services.wm.addListener(windowListener);
     };
 
     var stop = function() {
-        Services.ww.unregisterNotification(windowWatcher);
+        Services.wm.removeListener(windowListener);
 
         for ( var win of vAPI.tabs.getWindows() ) {
             onWindowUnload(win);
@@ -2976,6 +2977,11 @@ vAPI.contextMenu.register = function(doc) {
         return;
     }
 
+    // Already installed?
+    if ( doc.getElementById(this.menuItemId) !== null ) {
+        return;
+    }
+
     var contextMenu = doc.getElementById('contentAreaContextMenu');
 
     // This can happen (Thunderbird).
diff --git a/platform/opera/manifest.json b/platform/opera/manifest.json
index 1e6b79c76..d850eee97 100644
--- a/platform/opera/manifest.json
+++ b/platform/opera/manifest.json
@@ -2,7 +2,7 @@
     "manifest_version": 2,
 
     "name": "uBlock Origin",
-    "version": "1.3.1",
+    "version": "1.3.2",
 
     "default_locale": "en",
     "description": "__MSG_extShortDesc__",