You probably don't need this add-on. This extension is intended for people who used the 'passhash' extension authored by Steve Cooper. This is a very minimal webextension adaptation, that uses the exact same JavaScript code - and generates the exact same passwords.
Unlike other add-ons, this one does not attempt to find password fields on the active web page, or add buttons to them. When you want to generate a password, just click the toolbar button, type your password, Copy to clipboard, paste and press 'Wipe' to clear your clipboard of sensitive data.
Please only use this extension to migrate old passwords to newer, safer methods.