Mozilla has backtracked on its decision to remove an "experimental" Firefox add-on.

Last week, the company reported that two add-ons available for download, Sothink Video Downloader 4.0 and all versions of Master Filer, contained a Trojan horse. However, the company admits now it made a mistake - Sothink Video Downloader was not malicious after all.

"Since that disclosure, we've worked with security experts and add-on developers to determine that the suspected trojan in Version 4.0 of Sothink Video Downloader was a false positive and the extension does not include malware," according to a statement on a company blog.

Apologizing for the confusion, the company has re-enabled Sothink Video Downloader on AMO. However, the Master Filer extension in question is still considered malicious and is believed to have affected some 700 users.

"I don't think that Mozilla was wrong to withdraw the add-on from availability while its status was under question, but I do think there should have been more checking before publicly labelling it malware," blogged Graham Cluley, senior technology consultant at Sophos.