Examine source code of Preview Docs

{
  "manifest_version": 2,
  "name": "PreviewDocs",
  "version": "0.5.6resigned1",
  "description": "Preview documents, videos, music and more before you download them.",
  "options_ui": {
    "page": "settings.html",
    "browser_style": false
  },
  "permissions": [
    "*://*/*"
  ],
  "background": {
    "scripts": [
      "js/background.js"
    ]
  },
  "web_accessible_resources": [
    "js/*",
    "css/*",
    "fonts/*",
    "img/*",
    "flv/*",
    "settings.html"
  ],
  "browser_action": {
    "default_icon": {
      "19": "img/icon19.png",
      "38": "img/icon38.png"
    },
    "default_title": "PreviewDocs hasn't loaded on this page yet."
  },
  "applications": {
    "gecko": {
      "id": "@firepeek",
      "strict_min_version": "57.0"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "*://*/*"
      ],
      "all_frames": true,
      "js": [
        "js/jquery-3.3.1.js",
        "js/tooltipster.bundle.js",
        "js/contentscript.js"
      ],
      "css": [
        "css/tooltipster.bundle.css",
        "css/tooltipster-peek.css"
      ],
      "run_at": "document_end"
    }
  ],
  "icons": {
    "16": "img/icon16.png",
    "32": "img/icon32.png",
    "48": "img/icon48.png",
    "128": "img/icon128.png"
  }
}