Malicious Firefox and Chrome Add-ons

This threat uses fake extensions for both browsers to infiltrate user systems and hijack social media accounts – specifically, Facebook, Google+, and Twitter accounts. To install these fake extensions, users would see various lures on social media sites to try to get users to install a fake video player update.

Read more here - http://blog.trendmicro.com/trendlabs-security-intelligence/malware-hijacks-social-media-accounts-via-browser-add-ons/