Fix popup communication on Firefox

src/background.ts

@@ -84,7 +84,20 @@ chrome.runtime.onMessage.addListener(function (request, _, callback) {
         case "unregisterContentScript": 
             unregisterFirefoxContentScript(request.id)
             return false;
-    }
+        case "tabs":
+            chrome.tabs.query({
+                active: true,
+                currentWindow: true
+            }, tabs => {
+                chrome.tabs.sendMessage(
+                    tabs[0].id,
+                    request.data,
+                    (response) => callback(response)
+                );
+            }
+            );
+            return true;
+	}
 });
 
 //add help page on install

src/popup.ts

@@ -22,13 +22,15 @@ class MessageHandler {
     sendMessage(id: number, request: Message, callback?) {
         if (this.messageListener) {
             this.messageListener(request, null, callback);
-        } else {
+        } else if (chrome.tabs) {
             chrome.tabs.sendMessage(id, request, callback);
+        } else {
+            chrome.runtime.sendMessage({ message: "tabs", data: request }, callback);
         }
     }
 
     query(config, callback) {
-        if (this.messageListener) {
+        if (this.messageListener || !chrome.tabs) {
             // Send back dummy info
             callback([{
                 url: document.URL,