The TOTP shared key should be in base32 format, e.g. TK7P33KPE527ZTOX (github) or opid zgaw quda ip7q tj3z izo7 oemp t7dm (google).

The User field is not used for computing the TOTP; its only purpose is to act as a label for the password manager.

If the Save.. button does not pop up the Save login/password dialog, look for a key-like icon in the address bar or password input box and click on it.

Saving keys will not work if you have disabled Ask to save logins and passwords for websites in about:preferences#privacy in firefox, or if you're accessing this page via file:// in chrome.

This is a javascript implementation of a TOTP generator, using the browser's crypto API. It should do the exactly same thing as the google authenticator or any other TOTP generating app.

The javascript code does not send to or fetch any data from anywhere remotely, and the demo page should work the same when served over https, saved locally or used inside a browser extension.

I have also packaged this into an xpi firefox browser extension, which offers the convenience of generating the TOTP (for a key you have saved) directly from a toolbar popup instead of having to switch to another tab. The xpi does not do anything more than that and does not include any content scripts or filters.