Examine source code of mHeaderControl

{
  "manifest_version": 2,
  "name": "mHeaderControl",
  "version": "1.0.8resigned1",
  "description": "mHeaderControl is a Firefox Plugin which provides a bunch of features to manipulates HTTP headers of requests.",
  "icons": {
    "48": "icons/default-48.png"
  },
  "permissions": [
    "tabs",
    "storage",
    "webNavigation",
    "webRequest",
    "webRequestBlocking",
    "<all_urls>"
  ],
  "browser_action": {
    "default_icon": "icons/default-48.png",
    "default_title": "mHeaderControl",
    "default_popup": "popup/popup.html"
  },
  "background": {
    "scripts": [
      "common/library.js",
      "background/library.js",
      "background/background.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{2d083de0-ad91-4c1a-8e0c-5af7ff708b60}"
    }
  }
}