I came across and installed this tool from mozdev.com that protects Firefox (1.5 or higher) against common browser based attacks on malicious sites. You can create your own rules and block off anomalies if you know how to script the rules out.
The product is currently in Alpha (pre-beta, pre-release), so take all necessary precautions when using in production environments. The rules are taken off and simplified from Snort (http://www.snort.org), the open source Intrusion Detection System.
Check it out: http://firekeeper.mozdev.org