Examine source code of OnlyFollowedTweets

{
  "manifest_version": 2,
  "name": "OnlyFollowedTweets",
  "version": "1.3resigned1",
  "description": "Removes tweets in your timeline that don't belong there, such as tweets liked by people you follow.",
  "content_scripts": [
    {
      "matches": [
        "http://www.twitter.com/",
        "https://twitter.com/"
      ],
      "js": [
        "jquery-3.2.1.min.js",
        "content.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{de9ecc1f-aeb5-4f6a-aacb-fb32bec858c4}"
    }
  }
}