Technical answer to !extension: user scripting, e.g. Greasemonkey or Tampermonkey. Not quite as easy to deliver as an extension, but provides greater power such as opt-in violation of same origin policy and global variables shared across execution contexts.<p>The nice thing about user scripts is that there is no packaging or bundling. The advantage of Greasemonkey over Tampermonkey is it uses files rather than storing scripts in a database.