Examine source code of DevProxy

{
  "manifest_version": 2,
  "name": "DevProxy",
  "version": "1.0",
  "browser_specific_settings": {
    "gecko": {
      "id": "devgeekuf3@mail.ru",
      "strict_min_version": "42.0"
    }
  },
  "description": "Used for debugging.",
  "icons": {
    "48": "icons/pen-48.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "permissions": [
    "<all_urls>",
    "webRequest",
    "webRequestBlocking"
  ]
}