Great addon! I prefer FireFTP over any FTP client, and I especially like its cross-platform compatibility and its freeness (in all senses :)
I also have a suggestion I'd like to post, but since there's no feedback form on the FireFTP site, I'll post it here.
I recently had to create a new profile in FIrefox, and I needed to backup and import my FireFTP settings from my old profile. This worked flawlessly, except it didn't save the programs I use to open files with when you right-click a file and Open with. I'd like to see an option on the backup form to save default applications.
It isn't exactly a problem, but I've had to reset these settings for the fourth time now, once when installing on Windows, once on Linux, once on a reset Firefox profile on Linux, and now on a reset profile on Windows. I'd really appreciate backing up of default programs!
The Best! You could have the option to only activate it separately. Because sometimes I want to access the FTP through the browser and not through the extension. And it's hard to have to disable the extension, restart Firefox for this.