You know that cool little loading icon on the top right in the Firefox browser? Apparently it's called a throbber and you can change the link it goes to when you click on it.
1) Type about:config in your Firefox address bar and hit enter.
2) In the Filter box, type browser.throbber.url (although, just typing throb should suffice).
3) Under Preference Name, there should be a listing for browser.throbber.url. Select the listing and then right click > modify. Change the value of the URL in the text field, hit OK and you're done.