The key will be how effectively mozilla keeps Firefox patched -- especially patching flaws before they become public.
But, no matter how you cut it, IE's real problem is Active X. Active X is a public exploit designed into the browser. Keeping safe while using IE requires careful adjustment of the chair-keyboard interface.
Anyone stupid enough to use ActiveX deserves what happens. I abandonded that garbage for good in 2000, or thereabouts, and refused many projects because the client insisted on it.
(Denny Crane: "I Don't Want To Socialize With A Pinko Liberal Democrat Commie. Say What You Like About Republicans. We Stick To Our Convictions. Even When We Know We're Dead Wrong.")