Mozilla does store the passwords encrypted, but unless you set a master password, it's more of an obfuscation, as the decryption key is stored in a key file next to logins file. If you set a master password that is sufficiently complex, you should be safe-ish, unless you are facing Mossad.
Also the article never really identified how the "patient zero" machine was infected in the first place. RDP brute force?