Wildmonkey

Typically, you can execute custom JavaScript code in the browser's DevTools > Console.

This extension implements functionality missing from browsers, to save custom JavaScript code that can:

* Automatically execute when the page loads.
* Manually execute with a button click.

This extension also supports CSS code, which is internally converted to JavaScript code for execution.

This extension is not a replacement for Greasemonkey, so it doesn't support Greasemonkey-specific code.