Examine source code of BlockMask

{
  "manifest_version": 2,
  "name": "BlockMask",
  "version": "1.1",
  "description": "This is a plugin that allows you to verify the integrity of content, storaged in Social networks",
  "icons": {
    "16": "images/icon-16.png",
    "48": "images/icons/border-48.png",
    "128": "images/icon-128.png"
  },
  "content_security_policy": "default-src * 'unsafe-inline' 'unsafe-eval'; script-src 'self' 'unsafe-eval'; object-src 'self'; style-src 'self' 'unsafe-inline' 'unsafe-eval';",
  "applications": {
    "gecko": {
      "id": "webextension_addon@block.io"
    }
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "*://twitter.com/*"
      ],
      "js": [
        "content.js"
      ],
      "all_frames": true
    }
  ],
  "browser_action": {
    "default_icon": {
      "19": "images/icon-19.png",
      "38": "images/icon-38.png"
    },
    "default_title": "BlockMask",
    "default_popup": "popup.html"
  },
  "permissions": [
    "*://*/*",
    "tabs",
    "webRequest",
    "webNavigation",
    "storage",
    "activeTab"
  ]
}