URL rewrite – How to prefix a URL with another URL in a web browser with the help of a bookmarklet?

There is a web service called outline.com. You paste the URLs into this website and the page is reloaded into a neat formatting without unnecessary files from the original page. Another method is to prefix the URL of any Web site you are on with "outline.com/".

I would like to know if I can have a bookmark (let) that will do it automatically for me.

For example. if I'm on http: www.testsite.com, clicking on the bookmark should create outline.com/http:www.testsite.com.

I'm using the latest Safari post-Mojave-update.