From www.advrider.com:
ADVrider has a hardcoded list of web browsers to the extended interface to, which is terrible terrible terrible. If you change Firefox to advertise itself as Chrome (via general.useragent.override), ADVrider.com falls back to the dumb-browser interface.
ADVrider.com needs to do better browser sniffing. It has hardcoded Safari as supported, but not extended it to other WebKit browsers such as Chrome. The easiest way to do so without overhauling your broken sniffing system, is to search HTTP_USER_AGENT for WebKit or KHTML, so that you do not have to keep updating this hardcoded list for each KHTML or Webkit based browser that is released.