Messenger Preview

manifest.json

{
  "update_url": "https://clients2.google.com/service/update2/crx",
  "name": "Messenger Preview",
  "version": "0.1",
  "description": "Preview the appearance of messages sent in Facebook Messenger. Know how bold, italics, strikethrough, code, and math will appear.",
  "permissions": [
    "*://www.messenger.com/**",
    "*://www.facebook.com/messages/**"
  ],
  "icons": {
    "128": "images/icon128.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://www.messenger.com/t/*",
        "*://www.facebook.com/messages/**"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "web_accessible_resources": [
    "script.js"
  ],
  "manifest_version": 2
}