The update only applies to Ubuntu 12.10 (Quantal Quetzal)
On December 13, Canonical published in a security notice details about a unity-firefox-extension vulnerability for its Ubuntu 12.10 (Quantal Quetzal) operating system.According to Canonical, unity-firefox-extension (Firefox extension for Unity Integration) could have been made to expose sensitive information over the network.
It was discovered that unity-firefox-extension bypassed the same origin policy checks in certain circumstances.
If a user were tricked into opening a malicious page, an attacker could have exploited that to steal confidential data or perform other security-sensitive operations.
For a more detailed description of the security problems, you can visit Canonical's security notification.
Users can simply fix the security flaws by upgrading the operating systems to the latest xul-ext-unity package.
A normal system update, executed with the Update Manager, will implement all the necessary changes. A complete system restart is not necessary.