One of the best firefox addons you will ever find Rated 5 out of 5 stars

The simplest and most intuitive FTP tool ever.I have been using this tools for a long time now and it is just great!! It has never failed on me!

This review is for a previous version of the add-on (2.0.14). 

What's the issue you're having? Do you mean Firefox 21 compatible? (instead of 12)