Examine source code of Container In Title

{
  "manifest_version": 2,
  "name": "Container In Title",
  "description": "Modifies the Firefox window title to prepend the current tab's container, if it exists. For filtering/categorizing in time-tracking software, among other things",
  "version": "0.0.1",
  "icons": {
    "64": "icons/container-to-title.png"
  },
  "background": {
    "scripts": [
      "background_script.js"
    ]
  },
  "permissions": [
    "tabs",
    "contextualIdentities",
    "cookies"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{220d013f-ca2e-42dc-8438-de3f4cb7b986}"
    }
  }
}