This website reminds me of some of my winning jackpots and web browsing mining. I don't know why this website closed the web mining but I still miss that feature and I wish and the developer brings it back.
Web mining thing was removed long time ago. If I'm not mistaken, main reason of removal is antivirus programs - they don't like CPU mining and give warnings to users about it. I think that one of antivurus programs even blocked acces to Freebitco.in. So, it's not very likely that they're going to bring web mining back.
That was the reason at the time. They flag websites as malicious if they contain browser mining but even if that hadn't happened Coinhive shut down not long after so it would have gone then.