With the release of Safari 5, Apple will provide Safari developers with tools to create a digital certificate for extensions. Safari extensions must be signed with an Apple-provided digital certificate. The certificate protects the extensions from tampering and ensures that updates come only from the developer that owns it.
In addition, Safari extensions include built-in defenses like sandboxing which safeguards extensions from being used to access information on a user’s system. Built with standard web technologies, Safari extensions execute right in the browser, reducing the chance of an extension causing crashes or instability.
In addition to new security features and functions, Apple also fixed other vulnerabilities including CSS history hacks, potential HTTPS to HTTPS data leaks and more. A full detail of the security content for Safari 5 is available here.
Safari 5 is available for download at: http://www.apple.com/safari/download/