Examine source code of Bing for Firefox

{
  "manifest_version": 2,
  "name": "Bing for Firefox",
  "version": "1.0",
  "description": "Changes the user agent to xxx for all requests to bing.com",
  "permissions": [
    "webRequest",
    "webRequestBlocking",
    "https://*.bing.com/*"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{4446ff53-2814-460a-bae3-c791c0f2cf51}"
    }
  }
}