You don't really[1] need to install this, if you're using Firefox. Just set the prefs 'security.webauth.u2f' and 'security.webauth.u2f_enable_softtoken' to true.
[1] (Unless you need the token to live in your Mac OS keychain, instead of the Firefox profile directory.)
[1] (Unless you need the token to live in your Mac OS keychain, instead of the Firefox profile directory.)