Examine source code of Reading Ruler

{
  "manifest_version": 2,
  "name": "__MSG_extensionName__",
  "version": "1.8",
  "description": "__MSG_extensionDescription__",
  "developer": {
    "name": "Oren Trutner",
    "url": "https://github.com/orentrutner/reading-ruler"
  },
  "default_locale": "en",
  "permissions": [
    "storage",
    "tabs"
  ],
  "icons": {
    "48": "icons/ruler-48.png",
    "96": "icons/ruler-96.png",
    "128": "icons/ruler-128.png"
  },
  "page_action": {
    "browser_style": true,
    "default_icon": {
      "48": "icons/ruler-48.png",
      "96": "icons/ruler-96.png",
      "128": "icons/ruler-128.png"
    },
    "default_popup": "popup/popup.html",
    "show_matches": [
      "http://*/*",
      "https://*/*"
    ]
  },
  "commands": {
    "toggle-addon": {
      "suggested_key": {
        "default": "Alt+R"
      },
      "description": "Toggle Reading Ruler on or off"
    }
  },
  "background": {
    "scripts": [
      "src/polyfills/browser-polyfill.min.js",
      "src/common/colors.js",
      "src/common/commands.js",
      "src/common/extension.js",
      "src/common/options.js",
      "src/background/background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "http://*/*",
        "https://*/*"
      ],
      "css": [
        "css/main.css"
      ],
      "js": [
        "src/polyfills/browser-polyfill.min.js",
        "src/common/colors.js",
        "src/common/commands.js",
        "src/common/extension.js",
        "src/common/options.js",
        "src/content/range.js",
        "src/content/rect.js",
        "src/content/polyfills.js",
        "src/content/dom.js",
        "src/content/caret.js",
        "src/content/highlight-visualizer.js",
        "src/content/iframe-visualizer.js",
        "src/content/negative-visualizer.js",
        "src/content/ruler.js",
        "src/content/main.js"
      ],
      "all_frames": true
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{e1cad622-f77c-4035-8137-33b8296e5c9d}"
    }
  }
}