Examine source code of Exif Viewer

{
  "manifest_version": 2,
  "name": "Exif Viewer",
  "version": "3.7.6resigned1",
  "applications": {
    "gecko": {
      "id": "exif_viewer@mozilla.doslash.org"
    }
  },
  "default_locale": "en_CA",
  "description": "Displays the EXIF and IPTC metadata stored in JPEG files.",
  "icons": {
    "48": "exif.svg",
    "96": "exif.svg"
  },
  "background": {
    "scripts": [
      "content/code/overlay-webext.js"
    ]
  },
  "permissions": [
    "activeTab",
    "contextMenus",
    "storage",
    "<all_urls>"
  ]
}