diff --git a/js/contentscript-end.js b/js/contentscript-end.js
index bafa2bdb9..4c1801f83 100644
--- a/js/contentscript-end.js
+++ b/js/contentscript-end.js
@@ -30,7 +30,6 @@
 
 var uBlockMessaging = (function(name){
     var port = null;
-    var dangling = false;
     var requestId = 1;
     var requestIdToCallbackMap = {};
     var listenCallback = null;
@@ -50,9 +49,10 @@ var uBlockMessaging = (function(name){
         if ( !callback ) {
             return;
         }
-        callback(details.msg);
+        // Must be removed before calling client to be sure to not execute
+        // callback again if the client stops the messaging service.
         delete requestIdToCallbackMap[details.id];
-        checkDisconnect();
+        callback(details.msg);
     };
 
     var start = function(name) {
@@ -67,20 +67,30 @@ var uBlockMessaging = (function(name){
                     )
         });
         port.onMessage.addListener(onPortMessage);
-    };
 
-    if ( typeof name === 'string' && name.length > 0 ) {
-        start(name);
-    }
+        // https://github.com/gorhill/uBlock/issues/193
+        port.onDisconnect.addListener(stop);
+    };
 
     var stop = function() {
         listenCallback = null;
-        dangling = true;
-        checkDisconnect();
+        port.disconnect();
+        port = null;
+        flushCallbacks();
     };
 
+    if ( typeof name === 'string' && name !== '' ) {
+        start(name);
+    }
+
     var ask = function(msg, callback) {
-        if ( !callback ) {
+        if ( port === null ) {
+            if ( typeof callback === 'function' ) {
+                callback();
+            }
+            return;
+        }
+        if ( callback === undefined ) {
             tell(msg);
             return;
         }
@@ -90,22 +100,30 @@ var uBlockMessaging = (function(name){
     };
 
     var tell = function(msg) {
-        port.postMessage({ id: 0, msg: msg });
+        if ( port !== null ) {
+            port.postMessage({ id: 0, msg: msg });
+        }
     };
 
     var listen = function(callback) {
         listenCallback = callback;
     };
 
-    var checkDisconnect = function() {
-        if ( !dangling ) {
-            return;
+    var flushCallbacks = function() {
+        var callback;
+        for ( id in requestIdToCallbackMap ) {
+            if ( requestIdToCallbackMap.hasOwnProperty(id) === false ) {
+                continue;
+            }
+            callback = requestIdToCallbackMap[id];
+            if ( !callback ) {
+                continue;
+            }
+            // Must be removed before calling client to be sure to not execute
+            // callback again if the client stops the messaging service.
+            delete requestIdToCallbackMap[id];
+            callback();
         }
-        if ( Object.keys(requestIdToCallbackMap).length ) {
-            return;
-        }
-        port.disconnect();
-        port = null;
     };
 
     return {
diff --git a/js/contentscript-start.js b/js/contentscript-start.js
index 2554bd19f..627205100 100644
--- a/js/contentscript-start.js
+++ b/js/contentscript-start.js
@@ -38,9 +38,8 @@
 
 // https://github.com/gorhill/httpswitchboard/issues/345
 
-var messaging = (function(name){
+var uBlockMessaging = (function(name){
     var port = null;
-    var dangling = false;
     var requestId = 1;
     var requestIdToCallbackMap = {};
     var listenCallback = null;
@@ -60,9 +59,10 @@ var messaging = (function(name){
         if ( !callback ) {
             return;
         }
-        callback(details.msg);
+        // Must be removed before calling client to be sure to not execute
+        // callback again if the client stops the messaging service.
         delete requestIdToCallbackMap[details.id];
-        checkDisconnect();
+        callback(details.msg);
     };
 
     var start = function(name) {
@@ -77,20 +77,30 @@ var messaging = (function(name){
                     )
         });
         port.onMessage.addListener(onPortMessage);
-    };
 
-    if ( typeof name === 'string' && name.length > 0 ) {
-        start(name);
-    }
+        // https://github.com/gorhill/uBlock/issues/193
+        port.onDisconnect.addListener(stop);
+    };
 
     var stop = function() {
         listenCallback = null;
-        dangling = true;
-        checkDisconnect();
+        port.disconnect();
+        port = null;
+        flushCallbacks();
     };
 
+    if ( typeof name === 'string' && name !== '' ) {
+        start(name);
+    }
+
     var ask = function(msg, callback) {
-        if ( !callback ) {
+        if ( port === null ) {
+            if ( typeof callback === 'function' ) {
+                callback();
+            }
+            return;
+        }
+        if ( callback === undefined ) {
             tell(msg);
             return;
         }
@@ -100,22 +110,30 @@ var messaging = (function(name){
     };
 
     var tell = function(msg) {
-        port.postMessage({ id: 0, msg: msg });
+        if ( port !== null ) {
+            port.postMessage({ id: 0, msg: msg });
+        }
     };
 
     var listen = function(callback) {
         listenCallback = callback;
     };
 
-    var checkDisconnect = function() {
-        if ( !dangling ) {
-            return;
+    var flushCallbacks = function() {
+        var callback;
+        for ( id in requestIdToCallbackMap ) {
+            if ( requestIdToCallbackMap.hasOwnProperty(id) === false ) {
+                continue;
+            }
+            callback = requestIdToCallbackMap[id];
+            if ( !callback ) {
+                continue;
+            }
+            // Must be removed before calling client to be sure to not execute
+            // callback again if the client stops the messaging service.
+            delete requestIdToCallbackMap[id];
+            callback();
         }
-        if ( Object.keys(requestIdToCallbackMap).length ) {
-            return;
-        }
-        port.disconnect();
-        port = null;
     };
 
     return {
@@ -189,6 +207,9 @@ var netFilters = function(details) {
 };
 
 var filteringHandler = function(details) {
+    // The port will never be used again at this point, disconnecting allows
+    // the browser to flush this script from memory.
+    uBlockMessaging.stop();
     if ( !details ) {
         return;
     }
@@ -213,7 +234,7 @@ var hideElements = function(selectors) {
     }
 };
 
-messaging.ask(
+uBlockMessaging.ask(
     {
         what: 'retrieveDomainCosmeticSelectors',
         pageURL: window.location.href,
@@ -225,14 +246,6 @@ messaging.ask(
 /******************************************************************************/
 /******************************************************************************/
 
-// The port will never be used again at this point, disconnecting allows
-// the browser to flush this script from memory.
-
-messaging.stop();
-
-/******************************************************************************/
-/******************************************************************************/
-
 })();
 
 /******************************************************************************/
diff --git a/js/element-picker.js b/js/element-picker.js
index be05c0269..c818a296b 100644
--- a/js/element-picker.js
+++ b/js/element-picker.js
@@ -117,7 +117,6 @@
 
 var messaging = (function(name){
     var port = null;
-    var dangling = false;
     var requestId = 1;
     var requestIdToCallbackMap = {};
     var listenCallback = null;
@@ -137,9 +136,10 @@ var messaging = (function(name){
         if ( !callback ) {
             return;
         }
-        callback(details.msg);
+        // Must be removed before calling client to be sure to not execute
+        // callback again if the client stops the messaging service.
         delete requestIdToCallbackMap[details.id];
-        checkDisconnect();
+        callback(details.msg);
     };
 
     var start = function(name) {
@@ -154,20 +154,30 @@ var messaging = (function(name){
                     )
         });
         port.onMessage.addListener(onPortMessage);
-    };
 
-    if ( typeof name === 'string' && name.length > 0 ) {
-        start(name);
-    }
+        // https://github.com/gorhill/uBlock/issues/193
+        port.onDisconnect.addListener(stop);
+    };
 
     var stop = function() {
         listenCallback = null;
-        dangling = true;
-        checkDisconnect();
+        port.disconnect();
+        port = null;
+        flushCallbacks();
     };
 
+    if ( typeof name === 'string' && name !== '' ) {
+        start(name);
+    }
+
     var ask = function(msg, callback) {
-        if ( !callback ) {
+        if ( port === null ) {
+            if ( typeof callback === 'function' ) {
+                callback();
+            }
+            return;
+        }
+        if ( callback === undefined ) {
             tell(msg);
             return;
         }
@@ -177,22 +187,30 @@ var messaging = (function(name){
     };
 
     var tell = function(msg) {
-        port.postMessage({ id: 0, msg: msg });
+        if ( port !== null ) {
+            port.postMessage({ id: 0, msg: msg });
+        }
     };
 
     var listen = function(callback) {
         listenCallback = callback;
     };
 
-    var checkDisconnect = function() {
-        if ( !dangling ) {
-            return;
+    var flushCallbacks = function() {
+        var callback;
+        for ( id in requestIdToCallbackMap ) {
+            if ( requestIdToCallbackMap.hasOwnProperty(id) === false ) {
+                continue;
+            }
+            callback = requestIdToCallbackMap[id];
+            if ( !callback ) {
+                continue;
+            }
+            // Must be removed before calling client to be sure to not execute
+            // callback again if the client stops the messaging service.
+            delete requestIdToCallbackMap[id];
+            callback();
         }
-        if ( Object.keys(requestIdToCallbackMap).length ) {
-            return;
-        }
-        port.disconnect();
-        port = null;
     };
 
     return {
diff --git a/js/messaging-client.js b/js/messaging-client.js
index 740c53a5b..a9313f0be 100644
--- a/js/messaging-client.js
+++ b/js/messaging-client.js
@@ -42,7 +42,6 @@
 
 var messaging = (function(name){
     var port = null;
-    var dangling = false;
     var requestId = 1;
     var requestIdToCallbackMap = {};
     var listenCallback = null;
@@ -62,9 +61,10 @@ var messaging = (function(name){
         if ( !callback ) {
             return;
         }
-        callback(details.msg);
+        // Must be removed before calling client to be sure to not execute
+        // callback again if the client stops the messaging service.
         delete requestIdToCallbackMap[details.id];
-        checkDisconnect();
+        callback(details.msg);
     };
 
     var start = function(name) {
@@ -79,20 +79,30 @@ var messaging = (function(name){
                     )
         });
         port.onMessage.addListener(onPortMessage);
-    };
 
-    if ( typeof name === 'string' && name.length > 0 ) {
-        start(name);
-    }
+        // https://github.com/gorhill/uBlock/issues/193
+        port.onDisconnect.addListener(stop);
+    };
 
     var stop = function() {
         listenCallback = null;
-        dangling = true;
-        checkDisconnect();
+        port.disconnect();
+        port = null;
+        flushCallbacks();
     };
 
+    if ( typeof name === 'string' && name !== '' ) {
+        start(name);
+    }
+
     var ask = function(msg, callback) {
-        if ( !callback ) {
+        if ( port === null ) {
+            if ( typeof callback === 'function' ) {
+                callback();
+            }
+            return;
+        }
+        if ( callback === undefined ) {
             tell(msg);
             return;
         }
@@ -102,22 +112,30 @@ var messaging = (function(name){
     };
 
     var tell = function(msg) {
-        port.postMessage({ id: 0, msg: msg });
+        if ( port !== null ) {
+            port.postMessage({ id: 0, msg: msg });
+        }
     };
 
     var listen = function(callback) {
         listenCallback = callback;
     };
 
-    var checkDisconnect = function() {
-        if ( !dangling ) {
-            return;
+    var flushCallbacks = function() {
+        var callback;
+        for ( id in requestIdToCallbackMap ) {
+            if ( requestIdToCallbackMap.hasOwnProperty(id) === false ) {
+                continue;
+            }
+            callback = requestIdToCallbackMap[id];
+            if ( !callback ) {
+                continue;
+            }
+            // Must be removed before calling client to be sure to not execute
+            // callback again if the client stops the messaging service.
+            delete requestIdToCallbackMap[id];
+            callback();
         }
-        if ( Object.keys(requestIdToCallbackMap).length ) {
-            return;
-        }
-        port.disconnect();
-        port = null;
     };
 
     return {