FireFox as a Security Risk Compared to IE?

「はてな」の海外版のような Slashdot 11/26 に、次のような質問が出ていた。

A not-so anonymous Anonymous Coward asks: "The administrator at my work gave me the following reason for not using Mozilla. What do you think? 'FireFox is a security risk. Please refrain from using it. Please continue to use IE 6.0. IE is our only supported browser. FireFox saves encrypted pages to disk and does not give you override capability. It also does not allow automatic cache clearing when closing a browser. These are security risks.'" Do any of you have information that could be used to contradict the administrators information on FireFox? Are there configuration options one can reach from about:config that a user can use to address the problem this administrator has cited?

http://ask.slashdot.org/article.pl?sid=04/11/24/1841232

要するに、Firefox は、次の二点でセキュリティー上の危険があるから、IE を使うように上司から指示されたが、これに対する反論を求む、という内容。
１．暗号化したページをディスクに記憶させ、その機能を無効にできない
２．ブラウザーを閉じたときにキャッシュを自動的に消去できない