JB- Understand that the following is just my experience, so feel free to totally disregard (I won't mind, but also won't Date you...)
1). With respect to Cryptocurrency, it is important to note that as the underlying commodity increases, the interest in that commodity also increases; as that Commodity tanks, so does interest. So although Bitcoin mining was at its height in December 2017 (when BC hit a touch over 19,000USD), mining is of less interest today with BC price stabilizing at around 8000 USD.
2). Both Nvidia and AMD, whose Graphic Chips are used in Mining, have both stated in their recent earnings reports that they expect the demand for their chips used for Mining to decrease. Whether or not this is due to decreased interest in Mining (after all, there are a finite number of coins to be mined) or just an increase in usage of Bitmain Technologies ASIC chips is unknown (God, I wish, wish, wish that Bitmain Tech was a Publicly traded company! Their revenue in 2017 was between 3-4 billion USD and they just concentrate on Mining).
3). But Whatever- many browsers are already natively cognizant of the decreasing number of websites that mine. As an example, I personally have switched my browser to MS Edge. Soon after doing this I saw somewhere that a bunch of Pirate Bay clones were Coin mining Pots. On browsing to them with Edge I got a warning and the browser refused to connect to those sites (the Nerve!!!!). The other browsers I used were less savvy.
(side-note here- I'm sure at this point some question my sanity in having Edge as a default browser since it will autostart with Windows. I guess this would be concern over what Edge is sending out. This does not in any way concern me because I also have Seamonkey and Firefox as alternative browsers- Seakmonkey's home page is Wall Street Journal, and FF's home page is Yahoo Finance. On both the latter browsers I am always (at least recently) confronted with ads from either Fortinet, from Fashionophile (handbags), or shoes from Giuseppe Zanotti (you would just DIE if you saw the cuties I ordered last week!). Anyway, I know that I am already tracked, and I kind of like it...).
4). My point (I actually have one)- with a current browser and some sort of ad blocker I personally would not worry about Mining sites. But just stay away from Porno (if you are male, as if...), Crack, and Gambling sites.