changing security

:THNK Hello, I am using Windows IE7 XP2000, - would like to use Comodo programs to clean up BB spyware possibilities on my pc, - a second opinion - am with Avast for some long months and Avira recently. Shall I uninstall current defence and will it be safe to use the (incompatible) IE/[Comodo - or - Shall I use Firefox - without changing IE settings - Will this be okay to have two different securities in two different browsers? Thanks.