hmm well you could try editing the pref in user.js ,
http://www.mozilla.org/support/firefox/edit go there to find out how to make it then insert this into your user.js
code:
/*sets the throbber url */
user_pref("browser.throbber.url","http://www.mozilla.org/products/firefox/");
/*sets homepage url */
user_pref("browser.startup.homepage","http://start.mozilla.org/firefox?client=firefox-a&rls=org.mozilla:en-US:official");