Even when using Mozilla...

September 06, Security Focus — Mozilla Firefox, SeaMonkey, Camino, and Thunderbird multiple remote vulnerabilities. The Mozilla Foundation has released thirteen security advisories specifying security vulnerabilities in Mozilla Firefox, SeaMonkey, Camino, and Thunderbird. These vulnerabilities allow attackers to: execute arbitrary machine code in the context of the vulnerable application; crash affected applications; runjava_script code with elevated privileges, potentially allowing the remote execution of machine code; gain access to potentially sensitive information.

For a complete list of vulnerable products: http://www.securityfocus.com/bid/18228/info
Solution: New versions of Firefox, SeaMonkey, Camino, and Thunderbird are available to address these issues. Most Mozilla applications have self_updating features that may be used to download and install fixes. Please see the referenced advisories for information on obtaining and applying fixes: http://www.securityfocus.com/bid/18228/references
Source: http://www.securityfocus.com/bid/18228/discuss