Examine source code of Display Image Inline

{
  "name": "Display Image Inline",
  "description": "Change the response content type and disposition to force images to open in the browser window",
  "version": "1.1",
  "manifest_version": 2,
  "author": "bojax",
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "permissions": [
    "<all_urls>",
    "webRequest",
    "webRequestBlocking"
  ],
  "applications": {
    "gecko": {
      "id": "displayImageInline@bojax"
    }
  }
}