I'm developing a browser(firefox) plug-in which essentially checks for malicious input. My current approach is to store all input fields sent in GET/POST requests, try to heuristically determine potential attack vectors and drop requests in case true positives are detected.
For data retrieval I've been thinking of implementing the functionality of tamper data. However, I cannot find a similar open source plug-in and developing one from scratch seems rather difficult(the only suggestions I've found refer to standalone proxies such as burpsuite and webscarab).
Any help would be greatly appreciated.