Great work @tf2 and welcome to the forum. I’ve edited your code slightly as there was a missing bracket. It also needed a second parameter added to replace(). Should work now!
(JS docs ref: http://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/replace)
I als added a line requirements: [url] which constrains the extension to only appear when the selection contains a web URL.
Worth noting that this removes the entire query part of the URL, not just tracking codes. But makign it target tracking specifically would be significantly more complicated!