Mime Čuvalo’s FireFTP is a free, full-featured, interactive FTP client that plugs into Mozilla Firefox as an add-on.
FireFTP offers support for FTP, FTPS, SFTP and can remember a large number of connection profiles. FireFTP supports integrity checks using MD5 and SHA1, file compression on the fly (i.e., “MODE Z”), support for most FireFox platforms, support for multiple languages and IPv6.
FireFTP’s official site is fireftp.mozdev.org.
BEST PRACTICE: File transfer vendors that offer FTP, FTPS and/or SFTP support in their server products should support the FireFTP extension to Firefox.