I've just discovered this popping up on some of our workstations as MS has sneakily pushed this out earlier than the announced date (w/o 1st March), annoying as FF and (all?) google software installs in the user profile and doesn't need local admin rights to do so. I have denied it in the KB Override in Patch management, you might want to too.

Links:
http://support.microsoft.com/kb/976002

http://microsoftontheissues.com/cs/blogs/mscorp/archive/2010/02/19/the-browser-choice-screen-for-europe-what-to-expect-when-to-expect-it.aspx

Legacy Forum Name: Browser choice (KB976002),
Legacy Posted By Username: richardprice