Firefox always use DoH even when you disable it

Re:Firefox always use DoH even when you disable it by Bender on Friday October 10, 2025 @10:42PM (#45546128)

Interesting. If network.trr.mode is set to 5 this should not be occurring. If there is no plan to use FF again then I suppose submitting a bug would be a waste of time. Perhaps others will run into whatever condition is causing this behavior or perhaps it would happen on mine and my blackhole routes are breaking it.

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Re:Firefox always use DoH even when you disable it by fernvenue on Friday October 10, 2025 @10:46PM (#45546152)

Yep, that `network.trr.mode` is `5`, just confirmed. I'm considering Zen now.

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Re:Firefox always use DoH even when you disable it by Bender on Saturday October 11, 2025 @08:48AM (#45548756)

For what it's worth they have added a lot more outbound crap. Even using user.js [1] there is still a lot of leaky outbound noise. Loads of connections to fastly, cloudfront and others. It has gotten worse with time. I would probably also consider using a different browser but I can not give up the addons I use in Firefox. I will just blackhole route those CDN's and see what breaks.

[1] - https://github.com/arkenfox/user.js

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Re:Firefox always use DoH even when you disable it by Bender on Saturday October 11, 2025 @11:44AM (#45550023)

Can you confirm the full technical method you were using to see DoH traffic? i.e. Destination IP/port/protocol

Suggested capture methods:

    tcpdump -p --dont-verify-checksums -i any -NNnntt -B32768 -c2000 -s0 proto 6 and 'tcp[13] == 2' and not host ${Your_Router_IP} &

    tcpdump -p --dont-verify-checksums -i any -NNnntt -B32768 -c4000 -s0 proto 17 and not host ${Your_Router_IP} and 'length <256' &

Don't paste the output, just suggestions for capturing HTTPS SYN and QUIC over UDP.

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