Rated 2 out of 5 stars

Up to 2.0.5 it all worked great, but with 2.0.6 there are no ftp accounts anymore and I can't even create new ones.

I'm not happy with that

This review is for a previous version of the add-on (2.0.6.1-signed). 

This is a known issue and I've worked up a new version to fix it. You can download the latest version here:
http://nightlight.ws/static/fireftp.xpi
It will be released officially on addons.mozilla.org soon.

Sorry for the bug and thanks for your patience while I worked on fixing it!