Browser JSGuard has successfully blocked quite a few JS-Malware encoded scripts and other issues over the few years that i have been using it.

I've never had a false positive and until it detects a danger you don't even know that its there. So its one of my favorite security add-ons for Firefox as its fairly unique in what it does and is not a nuisance like most of the other security add-ons

My only wish was that i could also run this on the Firefox Android browser.