Examine source code of Save Image to Downloads

{
  "background": {
    "scripts": [
      "save_image_to_downloads.js"
    ]
  },
  "description": "Adds a right click direct download context menu item for images like on Safari.",
  "icons": {
    "16": "icon16.png",
    "48": "icon48.png",
    "128": "icon128.png"
  },
  "content_scripts": [
    {
      "js": [
        "save.js"
      ],
      "matches": [
        "http://*/*",
        "https://*/*"
      ],
      "run_at": "document_start",
      "all_frames": true
    }
  ],
  "manifest_version": 2,
  "name": "Save Image to Downloads",
  "permissions": [
    "activeTab",
    "downloads",
    "contextMenus",
    "tabs",
    "http://*/*",
    "https://*/*",
    "cookies",
    "storage",
    "management"
  ],
  "version": "1.0.1resigned1",
  "applications": {
    "gecko": {
      "id": "save_to_downloads@save_to_downloads.org"
    }
  }
}