Source: Yuki2718/adblockAbout CNAME tracker:
Update (2021-03-16): Many people now know AdGuard published CNAME tracker lists. As I wrote below, one should note even without such lists or CNAME uncloaking EasyPrivacy already blocked at least 70% of CNAME tracker all over the world. From the perspective of a filter author, CNAME tracker is no different from other tracker - we inspect script or request and if it sends unnecessary user data we block it unless doing so causes trouble. In fact, I was the first one opened an issue in the AdGuard's CNAME tracker repository to expand its coverage - some of CNAME tracker I proposed were not blocked not only by AdGuard but also by other services such as NextDNS because the trackers were unknown to them. CNAME uncloaking is done by checking the tracker's canonical name in known tracker database so is helpless against unknown tracker, and there are always such trackers out there.
I really don't understand why it's so special to some people. Apparently they still believe subscribing a dedicated anti CNAME tracker list is mandatory to block them if a DNS-level blocker is not deployed on an other layer. The fact is EasyPrivacy alone, or the combination of AdGuard Tracking Protection and my list, blocks about 70% of CNAME tracker while DEFINITELY many other analytics and trackers have slipped whatever your lists through, as long as you visit many sites. You prefer to double-lock a window and keep the door open? CNAME tracker is NOT at all harder to block and filter authors know much more serious circumvention. Of note, Google provides Server-side Tagging as announced in early 2020. This utilizes A or AAAA record, which is very well expected at the time of the CNAME fuss1. It's weird those who made fuss about CNAME cloaking seem to be silent about this. All these remind me that many people keep NoCoin despite EasyPrivacy + uBlock filters - Resource abuse covers 99% of them, and that others keep Adblock Warning Removal with a completely wrong assumption it has something to do with anti-adblock wall. Don't be fooled by misinformation on the Internet.
What about the difference for Opera only?As I know, the adblocker in Opera does't support all the syntax of block lists. I am not an expert, but it seems that it does't allow to use of scripts inside, which limits the ability to block some complex ads, but in most cases you will not see the difference. However, please note that only Brave and uBlock for Firefox can block CNAME trackers and ads, so it will be useful to install some secure DNS in Opera with support for filtering ads and trackers for an extra layer of privacy.
The only difference I notice is on the famous "adult" websites. Opera blocks the adds on the page, but when you click on a video, it opens a new tab with an add. That doesn't happen with uBlock.I'm not completely sure but I think the adblocker in Opera is less advanced.
So, in practice it could block less stuff.
If that doesn't bother you great, one extension less to deal with.
If you need more from an adblocker use uBlock Origin next to the buit-in Opera and you could uncheck the lists already used by Opera.
I haven't used classic Opera for a long time, but I don't think that they would make two different adblockers, most likely Opera and Opera GX work the same way.What about the difference for Opera only?
As I understand it, NextDNS will block the CNAME tracker based on the match of IP addresses in DNS records (maybe I'm wrong), which gives a larger coverage area than just a list of known CNAME trackers made manually for some list, so it can achieve not 70%, but maybe 90% of the blocks.