Could be Google is tracking past search history in order to try and find more relevant search results (e.g. your results in each browser depend on your past search history in that broswer – which is tracked with a cookie).

I tried with your example and got different results and then deleted the cookies in both IE and FF and then got exactly the same results (however none of the SERP included your site).

Of course that's my own SWAG (Scientific Wild A-- Guess)...