Examine source code of user-agent-rewriter

{
  "name": "user-agent-rewriter",
  "description": "Adds browser action icon to toggle user agent rewriting",
  "manifest_version": 2,
  "version": "1.0",
  "permissions": [
    "webRequest",
    "webRequestBlocking",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_title": "Toggle",
    "default_icon": {
      "16": "icons/mushroom_1f344_16.png",
      "32": "icons/mushroom_1f344_32.png",
      "48": "icons/mushroom_1f344_48.png",
      "128": "icons/mushroom_1f344_128.png"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "@emicba-user-agent-rewriter",
      "strict_min_version": "120.0"
    }
  }
}