Examine source code of Tweet2LowerCase

{
  "manifest_version": 2,
  "name": "Tweet2LowerCase",
  "version": "1.0.1",
  "description": "converts selected text to lowercase,on x.com, make it readable",
  "permissions": [
    "contextMenus",
    "activeTab",
    "tabs",
    "*://x.com/*"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": true
  },
  "browser_action": {
    "default_icon": "icon.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://x.com/*"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "icons": {
    "64": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{0fb9e14d-194c-45d9-832c-1324df34594e}"
    }
  }
}