Coin mining in the browser is interesting concept. Is this possible? Yes, just Google "Browser mining" and you'll see a lot of various sites and debates about this.
Here's the fresh site which offer mining via browser and the new coin, called JSEcoin (Java Script Enabled Coin).
User mining is just one of the options there.
Citation from the Whitepaper:
To make cryptocurrency fun, any user can log into their control panel and click a start mining button. Their browser will then be left to mine coins in the background while an iframe loads up a popular search engine and they can continue to browse the web as normal.
A dedicated coin pool will be offered so anyone with a web connection can go online and “earn” their fair share of the digital currency. This pushes the platform past “just being for webmasters and app developers”
The site is live and you can try it, here's the screenshot of mining platform:
I'm new in this, too, so any comments and discussion are welcome :)