Impulse requires at least Internet Explorer 7 to be installed in order to run (see the requirements here: http://www.impulsedriven.com/about.aspx).  This is due to the fact that Impulse uses Internet Explorer's web rendering engine to display any web based content (such as the store, community pages, EULAs for software, etc.)  If you use Firefox/Opera/etc. as your default web browser, please feel free to continue to do so.  Impulse simply requires that IE7 be installed, not that you make it your default browser or use it instead of other browsers.