Starting with Firefox 63 (scheduled for release in October 2018), Mozilla will provide protection against cryptomining websites by default, which is quite awesome. It will perform this by enabling tracking protection, blocking cross-site tracking cookies from gathering data on users.
Right now, if you want to stay away from cryptomining websites, you need to install a third party anti miner add-on (it works the same way as an adblocker), or add the mining websites inside your adblocker, so that they will not be resolved anymore.
Besides this, Mozilla will also add a few UI elements to make it easier for users to find tracking protection settings, to be easily turned on or off.
The tracking protection function is already present in Firefox, but it only blocks advertisment cookies, analytics and social sharing script and it won’t be able to block cryptomining websites until the update.
I am a big fan of Firefox, but I have switched to Palemoon browser on both Linux and Windows when Mozilla introduced the Australis interface and started to copy the Chrome design. But despite this, the extra layer of protection is quite needed and may enable Mozilla to make Firefox as ‘the most secured browser’, at least until others adopt the same features.
For more information, see this Bleeping Computer article.