"description": "Test",
 "permissions": ["tabs"],
 "manifest_version": 2,
 "name": "Test",
 "version": "1.0",

 "background": {
   "scripts": ["background.js"]
 },
    "applications": {
     "gecko": {
        "id": "test@test.com"
     }
  },
  
 "browser_action": {
   "default_icon": {
     "16": "icons/icon.png",
     "32": "icons/icon.png",

   }
 }

This is my manifest file: { "description": "Test", "permissions": ["tabs"], "manifest_version": 2, "name": "Test", "version": "1.0", "background": { "scripts": ["background.js"] }, "applications": { "gecko": { "id": "test@test.com" } }, "browser_action": { "default_icon": { "16": "icons/icon.png", "32": "icons/icon.png", "48": "icons/icon.png" } } } For some reason, attempting to use browser.tabs.Tab won't work. It just returns "undefined". It seems that the tabs permission isn't being given to background.js for some reason.