this fixes https://github.com/gorhill/uMatrix/issues/144

platform/chromium/vapi-client.js

@@ -21,8 +21,6 @@
 
 // For non background pages
 
-/* global self */
-
 /******************************************************************************/
 
 (function(self) {
@@ -136,6 +134,9 @@ vAPI.messaging = {
             },
             close: function() {
                 delete vAPI.messaging.channels[this.channelName];
+                if ( Object.keys(vAPI.messaging.channels).length === 0 ) {
+                    vAPI.messaging.close();
+                }
             }
         };