If it's the name of security, at least they could give some explanation of the real possibilities of taking advantage of a possible exploit, this is not the first time that the Mozilla team decides to alter features that come as defaults in the rest of the browsers without giving a proper explanation and/or (what's it's worse) documenting it. While it's nothing that the majority of the users are going to miss, but in a way they're going against stablished standards just for a perceived increase in security.
<insert rant of angry Opera users for removing file extensions in the cache for the new version and access to the shell, without a mention in the changelog>
Personaly, i really can't understand why they've done that, and seriously hope Opera doesn't choose to do the same :(
Ssssh! Don't give ideas! ;)