how-to block ads
In FireFox if type about:config in your address bar it brings up a page of browser settings. Ever wonder what those settings are/do? wonder no longer, This page contains an extensive list of About:config entries
If you go to the following section you can see it tells you about the URL connected to the Throbber. Now if you go to about:config and click on browser.throbber.url you can change the URL the Thrrobber takes you to when clicked.
browser.throbber Settings for the browser's throbber
Specifies URI to load when browser throbber is clicked