Mozilla Fesses up to Infected Firefox Add-Ons
The add-ons were infected with Trojan horses.
The add-ons, Sothink Web Video Downloader 4.0 and all versions of Master Filer, were infected with Trojan horses that were designed to hijack Windows PCs. Mac and Linux users were not affected.
Mozilla has removed the add-ons from Firefox's official add-on download site, however, post-4.0 editions of Sothink Web Video Downloader still remain available on other download sites. The company is instructing users to remove the add-ons and run a virus scan to detect and delete the malware.