Great add-on but... Rated 4 out of 5 stars
Having the blank window problem with the latest version and ff22. Version 2.0.10 works but I get an error message when I want to create a new account. ...just realized, only the first start worked, now again blank window with old version as well.This review is for a previous version of the add-on (2.0.16).
Sorry that you've run into this issue. The new version of FireFTP is doing migration of an old account format to a new one. Unfortunately, there are some illegal characters that make it difficult to upgrade to the new format that Mozilla now requires. (specifically, the combination of trying to convert international characters and the '%' character creates problems).
If the latest version isn't working for you, you can try the following:
find your profile folder, here are instructions: http://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data (if you're on a Mac it'll be under: ~/Library/Application Support/Firefox/Profiles)
find the file in your profile folder called fireFTPsites.dat
remove the '%' characters found in the file.
remove any characters that start with \x,
remove any characters that might have umlauts (like ä)
install the latest version and readd the % characters back in later as needed. (not directly into the file, but via the regular FireFTP interface).
The same applies for the files you're trying to import. If you have further issues, email me http://nightlight.ws/mime/about/contact and I'll help further.
Again, sorry for the inconvenience,