Updated Mozilla has admitted it erred in labelling one of the two Firefox add-ons offered for download from its official add-on site as malign last week.
Warnings that version 4.0 of Sothink Video Downloader add-on was contaminated by a Trojan were wrong and down to a false positive triggered by an anti-virus scanner used by Mozilla rather than the presence of real malware. The add-on, withdrawn from download last week because of malware concerns, has now been restored.
In a blog posting on Tuesday, Mozilla apologised for the mix-up and confirmed the other add-on under suspicion, Master Filer, is infected by the Bifrose Trojan and remains blacklisted.
The open source browser firm thanked McAfee for helping it sort out the confusion. It's not clear whose scanner triggered the false alert in the first place.
Mozilla revised its estimates that 6,000 downloads of potentially infected downloads might have taken place radically downwards. It now reckons its site might have served up malware-laced Firefox plug-ins fewer than 700 times.
As previously reported, Master Filer was downloaded 600 times between September 2009 and January from Mozilla's official add-on site before potential problems were detected. A scanning tool used to check add-ons during the upload process failed to detect anything awry even though the password-stealing Trojan strain it was infected with has been detected by commercial scanners since October 2008.
Malware infection in Firefox add-ons is rare but not unprecedented. In May 2008, the open source browser supplier warned that a Vietnamese language pack for Firefox 2 was contaminated with adware. ®