Well, yes.
This article talks about a nice concept of "unpatched days", referring to the amount of time between exploits being developed for a vunerability, and that vunerability being patched.
As of today, Secunia reports that there are still 19 unpatched security flaws in IE, the most severe of which is rated "highly critical." Firefox has only 4 unpatched flaws, all of which are rated "less critical" or "not critical," the lowest severity rating. Opera has none.