Well I finally sussed it out, unbeknown to me I had Firefox configured to automatically update and it installed a module called SearchProtect and this was causing the redirect to Yahoo, I found it by looking in installed programs and sorting on install date and there it was installed with yesterdays date, I uninstalled it, rebooted and received the proper ASP error ( there was a problem in my code ) fixed the error and bingo I'm back in business, this is bad behaviour by the FF devs and I will be telling them this is not acceptable.