http://www.furaffinity.net/view/1234837 <-- original

To obtain ID number:

1) Right-click on your userpage, or on the page of any of your submissions and go to "View source"/"View page source". The result should be the same.

2) Close to the bottom, there will be a section like this:
~~~~~~~~~~~~~~~~~~~~
var visitor_data = {
user_id: "12345",
username: "lalalalala",
lower: "lalalalala"
};
~~~~~~~~~~~~~~~~~~~~