Firekeeper

Firekeeper is an Intrusion Detection and Prevention System for Firefox. It is able to detect, block and warn the user about malicious sites. Firekeeper uses flexible rules similar to Snort ones to describe browser based attack attempts. Rules can also be used to effectively filter different kinds of unwanted content. Other features include:

Ability to scan incoming Firefox traffic - HTTP(S) response headers, body and URL and to cancel processing of suspicious responses.
HTTPS and compressed responses are scanned after decryption/decompression.
Very fast pattern matching algorithm (taken directly from Snort).
Interactive alerts that give an ability to choose a response to detected attack attempt.
Ability to use any number of files with rules and to automatically load files from remote locations.

Requirements:

Windows 2000/XP/Vista, Firefox 1.5.0.0+