Everything is explained step by step by the LE client in manual mode, you don't need any knowledge for it.
Stop talking about a browser solution, it's an email based validation, it doesn't have anything to do with browsers. The manual mode of the LE client could be a website as well.
Additionally, it will only work as long as you have setup a mail server, not everybody has this.
Keys and tokens are a lot more secure.
You don't have to repeat that link. As far as I can see it's about client side certificates, not server side certificates. LE doesn't have any plans to support client certificates (yet). Additonally, private keys shouldn't ever leave the server they're generated on except for encrypted backups, so it doesn't make sense to generate them in your browser.
Especially if you don't need HTTPS, just use the LE client in standalone mode to obtain a certificate, it's really easy and straight forward and does't require a mail server nor any knowledge.