Security isn't the only improvement according to Reuters:

Additions boost security and allow users to run Web sites when they are not connected to the Internet. Mozilla also says Firefox 3 uses less computer memory than Firefox 2.

The security improvements identified in the release notes include:

• One-click site info: Click the site favicon in the location bar to see who owns the site. Identity verification is prominently displayed and easier to understand. In later versions, Extended Validation SSL certificate information will be displayed.


• Malware Protection: malware protection warns users when they arrive at sites which are known to install viruses, spyware, trojans or other malware. You can test it here (note: our blacklist of malware sites is not yet activated).


• New Web Forgery Protection page: the content of pages suspected as web forgeries is no longer shown. You can test it here.


• New SSL error pages: clearer and stricter error pages are used when Firefox encounters an invalid SSL certificate.


• Add-ons and Plugin version check: Firefox now automatically checks add-on and plugin versions and will disable older, insecure versions.


• Secure add-on updates: to improve add-on update security, add-ons that provide updates in an insecure manner will be disabled.


• Anti-virus integration: Firefox will inform anti-virus software when downloading executables.


• Vista Parental Controls: Firefox now respects the Vista system-wide parental control setting for disabling file downloads.

There is more on Firefox 3 beta in a previous post.