Examine source code of Already Seen

{
  "browser_specific_settings": {
    "gecko": {
      "id": "alreadyseen@ranosoft.net",
      "strict_min_version": "64.0"
    }
  },
  "description": "Grays out texts that you've already seen when previously visiting a particular page. To start monitoring a page, select some text, right click, and select \"Already Seen\".\n\nThis extension will help you quickly identify new elements on the sites you visit frequently. This is particularly helpful for lists or table rows, like a list of offers that appear daily. You will no longer be bothered by repeated offers, and will be able to always focus on the new ones only.",
  "manifest_version": 2,
  "name": "Already Seen",
  "version": "1.0.3",
  "icons": {
    "48": "icons/icon48.png",
    "64": "icons/icon64.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*/*"
      ],
      "js": [
        "alreadyseen.js"
      ]
    }
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "permissions": [
    "activeTab",
    "storage",
    "unlimitedStorage",
    "contextMenus",
    "downloads",
    "tabs",
    "notifications"
  ],
  "options_ui": {
    "page": "options.html",
    "browser_style": true
  }
}