The Opera web browser has joined Brave in allowing users to turn on ‘cryptojacking’ protection:

Bitcoins are really hot right now, but did you know that they might actually be making your computer hotter? Your CPU suddenly working at 100 percent capacity, the fan is going crazy for seemingly no reason and your battery quickly depleting might all be signs that someone is using your computer to mine for cryptocurrency.
For a very short period of time around five years ago I 'cryptojacked' visitors to my blog using JavaScript. Back then, Bitcoin was worth so little, and the slowdown for visitors was so great, that I soon turned it off.

Given the recent explosive rise in Bitcoin’s value, however, it would seem that cryptojacking is yet another thing to guard against online…

Source: Opera blog