MSIE was 98% unsafe. There were only 7 days in 2004 without an
unpatched publicly disclosed security hole.
Firefox was 15% unsafe. There were 56 days with an unpatched
publicly disclosed security hole. 30 of those days were a Mac
hole that only affected Mac users. Windows Firefox was 7%
Opera was 17% unsafe: 65 days. That number is accidentally a
little better than it should be, as two of the upatched periods
happened to overlap.