Browser differences Mozilla v IE

[Chris Lyon]

I've been developing CGI python scripts for generating web pages which
are served from IIS. I've been viewing them from IE successfully for
sometime now.
I've just downloaded and installed Mozilla and when I try to run the
same pages from Mozilla it trys to download them and run them in a DOS
window.
 I'm rateh confused can anyone shed any light on where I should be
tweaking to sort this out?