I'm an engineer on Facebook's product security team, fighting malware trying to infect Facebook users or abuse our products. I'm one of the folks that's been battling the recent rise in malicious browser extensions and I'm happy to talk about our fight against them. Many extensions provide users with a way to augment their web experience. However, there are some built solely to steal a person's personal information, spam, or inject ads to the webpages they visit.
As part of our response to this threat, we built a Javascript library that tries to load the manifest file from extensions we've seen exhibit malicious behavior. Based on the results of those attempts, we can provide the user with the means to remove the threat, including free anti-virus software to clean the infection.
We built this feature to fight the recent spate of malicious browser extensions focused on Facebook. We take the trust Facebook users put in our product seriously and are always innovating new products and features to protect their information.