Similarly you can run javascript programs on a site with a parameter from the url bar, if you want. For example you can make a bookmark with the URL javascr

Similarly you can run javascript programs on a site with a parameter from the url bar, if you want. For example you can make a bookmark with the URL javascript: document.body.innerHTML = "%s" + document.body.innerHTML and add a keyword @addBefore and it will work. (Useless example, but it probably shows where and how the javascript runs.)