Bad UI Rated 1 out of 5 stars
The crappy UI means I'd stick with the less-featured Fire Encrypter (https://addons.mozilla.org/en-US/firefox/addon/fire-encrypter/). A toolbar isn't an appropriate interface (especially as the only interface) for a tool that isn't in constant use - besides which the text input/output box should be more than one line high.
Isn't in constant use?
View -> Toolbar -> Uncheck CryptoFox Toolbar