Rated 4 out of 5 stars
I've been using FireFTP for a few years already. It is fast and reliable. Too bad it won't work with FF 6.0 Probably the developers could look into the problem and fix it.This review is for a previous version of the add-on (188.8.131.52-signed).
It does work with Firefox 6 - it's now found in Tools->Web Developer.