Mozilla issues warning that two add-ons available from AMO were infected by malicious code. The Master Filer add-on was infected by the LdPinch password-stealing Trojan. Sothink Web Video Downloader version 4.0 was also infected by a version of the Bifrose backdoor Trojan horse. Both Trojans were specifically written for Windows, meaning they could not infect on Mac OS X and Linux installations of Firefox. In May 2008, users who downloaded Firefoxs Vietnamese language pack were warned that it contained a malicious script.”]
Source: https://nakedsecurity.sophos.com/2010/02/05/mozilla-admits-firefox-addons-contained-trojan-code/