Firefox doesn't resolve dns correctly after v. 90.0

[holunde]

I use Firefox a LOT for my work as a sysadmin. And I use Linux Mint, because I don't want to spend time on my own workstation. Instead I can spend my time on server, switches and all that jazz - because Mint is soooo reliable. Really.

But about a week ago, when Firefox was updated to version 90, I started having problems connecting to some of my company's web-servers. We host them ourselves, and they are placed on a DMZ-like network-segment. So their ip-addresses are for example 192.168.0.2, when I access them from inside our LAN.
And from out on the internet they would have public addresse like 87.116.52.8 for example.
This is just fine and is handled correctly by our own dns-servers. So when I access intranet.mycompany.com from inside the LAN, dns gives my the ip 192.168.0.2 for example. And this works and has worked for everyone for years....
But from Firefox 90+ on Linux Mint this doesn't work anymore. Strangely.
The browser times out on these internal host-addresses. All other addresses work fine.
And even stranger, if I wipe my Firefox-profile COMPLETELY, the problem disappears. But returns after a few minutes of work.
I've confirmed this behaviour on my workstation and on a Mint-laptop, that I also use - several times.

The solution was to install a Flatpak-version of Firefox 90 on the same machines. No dns-problem. But the Flatpak-version has so many annoying restrictions that I instead jut downloaded a tar-version of Firefox 90.0.2 from mozilla.org, installed in my home-directory. No dns-problems.

But the Mint-version of Firefox 90+ has a problem resolving dns to private-space ip's.

Has anyone encountered this problem apart from me?

Danish summer-greetings
Hans Otto Lunde

[JoeFootball]

But the Mint-version of Firefox 90+ has a problem resolving dns to private-space ip's.

I don't have my own DNS to test this, but try going to Edit > Settings > General > Network Settings, and deselect "Enable DNS over HTTPS". Or keep it enabled and change the Provider to your DNS.

[dave0808]

I've the same Firefox version and run my own DNS server. Local addresses are resolved fine in FF90. As suggested above, the "DNS over HTTPS" may be enabled, so requests could be going to Cloudflare instead of your system configured servers.

You could also open a new tab and go to "about:config" then enter 'dns' into the search field to get a list of all the parameters that Firefox uses. As a sysadmin, you might see something amiss there.

[t42]

Edit > Settings > General > Network Settings, and deselect "Enable DNS over HTTPS".

That's "unexpected". I'm not using DoH, but going to https://www.dnsleaktest.com/ on FF 90.0.2 was presented with

Code: Select all

Servers found  ......		1
IP 	 	 	Hostname 	ISP
xxx.xxx.xxx.xxx 	None 		Cloudflare

Unchecking "Enable DNS over HTTPS" as in JoeFootball's comment returned me to my global DNS settings.

Code: Select all

Servers found  ......		4
IP 	 	 	Hostname 	ISP
172.253.xxx.xxx 	None 		Google

So without any warning the browser was removed from the system DNS (in my case it is encrypted DoT) and went to another protocol and company, all in secret from unsuspected user. This setting "Enable DNS over HTTPS" was explicitly unchecked by me in previous FF versions.

[JoeFootball]

... all in secret from unsuspected user.

Speaking for myself, I did get a browser notification telling me that it was enabled, with the option to disable.

Edit: https://support.mozilla.org/en-US/kb/fi ... over-https

[Moonstone Man]

... all in secret from unsuspected user.

Speaking for myself, I did get a browser notification telling me that it was enabled, with the option to disable.

I assume that's the problem. Nice pickup on your part if it is the problem.

[t42]

Speaking for myself, I did get a browser notification telling me that it was enabled, with the option to disable.

Thank you for that information about notification. After reading your comment I found three systems with FF 88 and FF 90. After update of FF on LM19.3 DoH was off. After update of FF on LM20.2 DoH was switched on without notification. Maybe my privacy oriented customized profile prevents that notification (something like FF studies disabled or something else) or it is a regional behavior (it is known that FF implemented DoT on regional basis). It is interesting that each new profile created on the 'affected' system had DoT off.

[holunde]

Thanks for the feedback.
I also suspected that Dns Over Https could be the cause, but the problem remained with DOH disabled.
I looked into a lot of dns-settings without any result. So I decided to leave it for now and just use the stok-Firefox.
It is strange, and I will report back when I find time to investigate more.

[doge-stonks]

Thank you. I had a similar problem where I couldn't access internal websites. It's version 94 already and disabling DNS over HTTPS solved my problem.