I'm using Pi-hole (running on a Raspberry Pi) as my DNS server. It uses several hosts files (and you can add even more) which block network requests to countless ad networks, trackers and malware sites system-wide. Its query log displays all network request and shows which of them are blocked or not. (Btw: an alternative solution is AdGuardHome). That query log is the reason why I can confidently say that uMatrix and uBlock Origin block/filter network requests reliably on Firefox which has been my default browser for a long time. But what about other browsers? Let's perform a test with Chromium and uMatrix and uBlock Origin (or with uBO alone in Hard Mode blocking mode if you want) and load www.washingtonpost.com. This is what the Pi-hole query log shows us: Oops! These are requests that should have been blocked by uM and/or uBO (and are now blocked by one of the hosts files in Pi-hole). However, if you started the uM or uBO logger before loading that site, the requests to, e.g., outbrain.com do not show up at all. Is this a problem of uM or uBO? I created a new Chromium profile and installed AdBlock Plus instead (and added some additional lists like EasyPrivacy). But the result is the same as above: There a blocked requests in Pi-hole which should have been blocked by the add-on. I repeated the tests with the Chromium-based browsers Vivaldi and Brave: The situation is no different than before which is especially interesting as both browsers come with their own built-in adblockers which were not able to filter these requests, either. Again, this problem does not occur in Firefox - but why in Chromium (-based browsers)? The answer is given in the uBlock Origin wiki: uBO offers the option to "Disable pre-fetching" (which was checked in my tests, of course). The wiki says: And now the important part: @gorhill found out that Note that a duplicate of the related Chromium bug is closed as "fixed". So either this fix is incomplete - or there is another bug that allows for this bypass. Note that I observed these bypasses only on few domains, and www.washingtonpost.com is one of them. But many other sites could also be affected - and most users don't notice because they do not use something like Pi-hole. This solution or a big hosts file in your system could mitigate these bypasses. Conclusion: If you care for your privacy don't use Chromium (-based browsers). Manifest 3 will make the situation even worse.