www.dslreports.com The certificate of the site is expired. See also https://www.ssllabs.com/ssltest/analyze.html?d=www.dslreports.com I hope for them that they can fix it soon! Best wishes over there!
I hope it too for them! PS: long ago, if there was a problem with one the sites, it was allowed to post it on the other site; just to inform and help.
This is how Firefox lists the certificates, to establish a valid trustworthy chain. First tab is the certificate issued to "dslreports" from "Let's Encrypt R3", valid from 25 Sep 2023 to 24 Dec 2023. The second tab is the certificate for "let's Encrypt R3" itself, that is issued by "ISRG Root X1", valid from 4 Sep 2020 to 15 Sep 2025. The third tab is a self signed certificate for "ISRG Root X1", valid from 4 Jun 2015 to 4 Jun 2035. Hope this clarifies the issue.