Please try the suggestions in the FTP doesn't work FAQ.
Make sure Opus is using the exact same settings as the other FTP clients which work with the firewall enabled, and try toggling the passive mode setting (try it in both states in case one works and the other doesn't).
Posting the FTP log (with any private details like IP addresses and system details blanked out) may also help us see what's wrong.
I can't reproduce that here.
Do you mean the FTP address book is already open, and you right-click an entry to show the context menu for it? Or are you right-clicking items in the FTP menu off the lister itself, and choosing Edit? Or right-clicking somewhere else? (Both those examples work OK here.)