Examine source code of RescueTime

{
  "manifest_version": 2,
  "name": "RescueTime for Firefox",
  "version": "3.3.0",
  "description": "Keep track of the time you spend in Firefox, and get a clear picture of what you were doing all day.",
  "homepage_url": "https://www.rescuetime.com",
  "applications": {
    "gecko": {
      "id": "rescuetime_firefox@rescuetime.com",
      "strict_min_version": "58.0"
    }
  },
  "icons": {
    "32": "icons/icon-32.png",
    "64": "icons/icon-64.png",
    "128": "icons/icon-128.png"
  },
  "permissions": [
    "tabs",
    "idle",
    "https://*.rescuetime.com/",
    "storage",
    "cookies"
  ],
  "browser_action": {
    "browser_style": true,
    "default_icon": "icons/icon-128.png",
    "default_title": "RescueTime",
    "default_popup": "popover.html"
  },
  "background": {
    "page": "background.html"
  }
}