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Expected Behaviour:
Firefox must not load ads
Actual Behaviour:
Firefox (63.0.3 x64) loads ads on several websites where Chrome and Edge are "clean". I already disabled dns-prefetch and network.trr in Firefox' config but the browsers keeps loading and showing ads on specific websites.
Look in the Firefox Preferences > General > Network Settings and ensure you don't have DNS over HTTPS enabled. If you enable this, the DNS requests will bypass your Pi-Hole.
Here is a good FAQ that will help you determine where the ads are coming from. Note that Pi-Hole logs will only show DNS requests that are processed by Pi-Hole (and won't show any that bypass Pi-Hole).
The first one (trr.mode) controls how *DoH* should be used. By default it is set to 0, meaning it is disabled. You can change it to "2" to enable it. The options for the trr.mode are:
* 0 — **Off** (default). To use operating system resolver.
* 1 — **Race** native against TRR. Do both in parallel and go with the one that returns a result first. Most likely the native one will win.
* 2 — **First** . Use TRR first, and only if the secure resolution fails use the operating system resolver.
* 3 — **Only** . Only use TRR. Never use the native (after the initial setup).
* 4 — **Shadow** . Runs the TRR resolves in parallel with the native for timing and measurements but uses only the native resolver results.
* 5 — **Off by choice** This is the same as 0 but marks it as done by choice and not done by default.
Neither "network.trr" set to "0" or "5" had any impact. I checked "about:networking#dns" and had no entry under "TRR" with "true". It's not a big thing because most ads are still blocked in Firefox. But it's interesting that Chrome and Edge don't show these ads.
I don't use any add-on in Firefox. It's a clean install. I set Firefox to clean every web data on close. I also tried the safe-mode but the effects are the same.
I tried this in another network where Pi-Hole is also active. Same effect: Firefox with no add-ons loads some ad elements, Chrome and Edge don't.
Pi-hole works on the DNS level and cannot block all ads. I strongly suggest to use uBlock Origin in your browser. I don't see ads on those sites. And if there are any which are not blocked by the filterlists, it's usually easy to block them with the Element Picker. This is often the case for cosmetic filtering.
I didn't think I see ads either (cannot read German), with Firefox latest version and no supplemental ad blocking by the browser. DNSThingy on Chrome didn't show any odd ad-serving domains either:
Yes, these images are always loaded from the corresponding website and not from any ad-server. Seems to be a new method of ad-delivery or anti-adblocking.