It's only supported in chrome, with other browser support at least 6 months away (guess). After getting a test webapp to work with u2f tokens on chrome I wouldn't say it's easy. YMMV.

You need to include this js: https://demo.yubico.com/js/u2f-api.js

... which isn't really mentioned anywhere. That js file loads an embedded chrome extension and handles all the heavy lifting.

The documentation (if there is any?) fails to mention that your appId has to be https; any http appIds will fail with an obscure error.