User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:78.0) Gecko/20100101 Firefox/78.0
Steps to reproduce:
When I visit rss.forumanalogue.fr or www.forumanalogue.fr, Firefox sometimes display toot.forumanalogue.fr instead.
The top image shows the first visit of rss.forumanalogue.fr, then I visit toot.forumanalogue.fr, see middle screenshot, and finally, I visit rss.forumanalogue.fr again, see bottom screenshot.
Sometimes Firefox is having a wrong IPv6 in cache. Using the extension SixOrNot, I can see for rss.forumanalogue.fr the following IPv6 2001:41d0:fecf:8900:216:3eff:fe65:97bc, with the label "Cache". However, this IP corresponds to toot.forumanalogue.fr and the actual IPv6 for rss.forumanalogue.fr is 2001:41d0:fecf:8900:216:3eff:fef1:20a2.
It is not linked to the extension SixOrNot. Indeed, I have the same issue with other computers on my network which don't have this extension installed.
They are also using different DNS resolvers, which makes me wonder if Firefox is ignoring the system DNS resolvers.
DoH is disabled.
For all tested computers, other web browsers are working properly, tested with w3m and Chromium.
I thought that it can come from DNS Prefetching, however, there is no X-DNS-Prefetch-Control in any of the HTTP headers for any of the involved website.
I guess that if it was about cache and cookies, the issue would not be random.
about:networking#dnslookuptool shows correct AAAA entries even when Firefox is having the wrong IPv6 in cache.
Firefox should have cached the IPv6 corresponding to the website, not another one.