Trojan for Firefox: Trojan.PWS.ChromeInject.A

Here are a news about trojan from Greasemonkey — a Firefox addon. It is identified by BitDefender.

BitDefender has identified this new bit of holiday cheer as Trojan.PWS.ChromeInject.A” (the ChromeInject suffix refers to the Chrome component of Firefox). The trojan installs itself into Firefox's add-on directory, registers itself as Greasemonkey, and begins searching your hard drive for passwords, login details, your World of WarCraft account information, and your library card number.
Please note, this trojan is not actually the Greasemonkey add-on, and only identifies itself as such. Mozilla has confirmed that the official Greasemonkey release contained within Mozilla's own extension repository (and available here) is malware-free. If you're currently using Greasemonkey or are interested in doing so, there's no reason to avoid the legitimate add-on at this time, so long as you download it from Mozilla's page or an equally trusted source.
Source

What does this trojan do?

Once installed, the trojan is capable of identifying over 100 web sites. When an infected user visits a site the trojan recognizes, the parasite comes to life and records the login/password details being transmitted. Presumably it then goes back to sleep, quietly keeping an eye on further system activity.