Seen Blocker

manifest.json

{
  "update_url": "https://clients2.google.com/service/update2/crx",
  "name": "Seen Blocker",
  "version": "1.0",
  "manifest_version": 2,
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "icons": {
    "16": "ico_16.png",
    "48": "ico_48.png",
    "128": "ico_128.png"
  },
  "description": "Blocks the 'Seen' feature on Facebook Messages.",
  "browser_action": {
    "default_icon": "ico_128.png",
    "default_popup": "popup.html"
  },
  "options_page": "options.html",
  "content_security_policy": "script-src 'self' https://ssl.google-analytics.com; object-src 'self'",
  "permissions": [
    "storage",
    "webRequest",
    "webRequestBlocking",
    "*://*.facebook.com/*",
    "*://*.messenger.com/*"
  ]
}