Issue 5386 - Ignore messages from content scripts in devtools panel

ext/content.js

 "use strict";
 
-chrome.runtime.onMessage.addListener((message, sender, sendResponse) =>
+// Firefox 55 erroneously sends messages from the content script to the
+// devtools panel:
+// https://bugzilla.mozilla.org/show_bug.cgi?id=1383310
+// As a workaround, listen for messages only if this isn't the devtools panel.
+if (!("devtools" in chrome))
 {
-  return !("tab" in sender) &&
-         ext.onMessage._dispatch(message, {}, sendResponse).indexOf(true) != -1;
-});
+  // Listen for messages from the background page.
+  chrome.runtime.onMessage.addListener((message, sender, sendResponse) =>
+  {
+    return ext.onMessage._dispatch(message, {}, sendResponse).includes(true);
+  });
+}
 
 (function()
 {
   let port = null;
 
   ext.onExtensionUnloaded = {
     addListener(listener)
     {
       if (!port)
         port = chrome.runtime.connect();
@@ skipping 10 matching lines @@
 
         if (!port.onDisconnect.hasListeners())
         {
           port.disconnect();
           port = null;
         }
       }
     }
   };
 }());