Update manifest.json

Author: Katsute

src/manifest.json

@@ -12,6 +12,12 @@
         "128": "icon128.png"
     },
 
+    "browser_specific_settings": {
+        "gecko": {
+            "id": "{3e7882e9-4411-4136-9c76-8fddc57c8d87}"
+        }
+    },
+
     "permissions": [],
     "content_scripts": [{
         "js": ["index.js"],