Rated 4 out of 5 stars
I did several short tests: Also works fine with SeaMonkey 2.33.1 (German Language pack) Gecko/20100101 Build 20150321194901 (Default Theme) on German WIN7 64bit.
Unfortunately install.rdf limits SeaMonkey compatibility to "maxVersion>2.17.*", so that users might expect that FireFTP will not work with latest SeaMoney Versions. It would be great if someone could patch that. And may be amend short description from "... client for Mozilla Firefox which ..." to "... client for Mozilla Firefox and SeaMonkey which ..."