Which add-ons can replace FireFTP ?
I don’t know about addons, but there are many FTP clients you can use.
I am happy with FileZilla and Cyberduck (this is for Mac). Filezilla is great because it’s multiplatform so you don’t have to learn new tricks if you use multiple operating systems.
I also just use FileZilla on Windows 10 and Ubuntu Linux. Never had problems with it. (but I must confirm I also never used FireFTP)