Most of the Trojans infects the legitimate websites with a script that points to a malicious source/script, when executed infects you system with the Trojan.
Recently my slambook site got infected with such script. So i want to trace that source, since it being a script i need to view the generated HTML code by that script. I found this Mozilla addon WebDeveloper, a superb addon that everyone needs to have for better control over websurfing.
Also this can be used for styling your websites.