Examine source code of Evernote Helper

{
  "description": "Enrich Evernote web ui",
  "manifest_version": 2,
  "name": "Evernote Helper",
  "version": "1.3",
  "homepage_url": "https://github.com/bladepan/EvernoteHelperFireFoxAddon",
  "icons": {
    "48": "icons/icon-48.png"
  },
  "permissions": [
    "activeTab"
  ],
  "browser_action": {
    "default_icon": "icons/icon-32.png",
    "theme_icons": [
      {
        "light": "icons/icon-32-light.png",
        "dark": "icons/icon-32.png",
        "size": 32
      }
    ],
    "default_title": "Evernote Helper",
    "default_popup": "popup/popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.evernote.com/client/web*"
      ],
      "js": [
        "content_scripts/content.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{0a90c519-61e7-4793-984d-d4ccb83e4cdd}",
      "strict_min_version": "42.0"
    }
  }
}