https://support.mozilla.org/en-US/kb/websites-say-cookies-are-blocked-unblock-them

Make sure you are not blocking content.

https://support.mozilla.org/en-US/kb/enhanced-tracking-protection-firefox-desktop also see https://blog.mozilla.org/security/2021/03/23/introducing-smartblock/

https://support.mozilla.org/en-US/kb/smartblock-enhanced-tracking-protection

Diagnose Firefox issues using Troubleshoot(Safe) Mode {web link}

A small dialog should appear. Click Start In Troubleshoot(Safe) Mode (not Refresh). Is the problem still there?

Many site issues can be caused by corrupt cookies or cache.

Warning ! ! This will log you out of sites you're logged in to. You may also lose any settings for that website.

• Delete cookies to remove the information websites have stored on your computer {web link}

• How to clear the Firefox cache {web link}

Sorry - the problem occurs with FF in safe mode, all cookies and history deleted, and standard privacy settings. It did not occur prior to version 96.

Does this only occur on

http://www.dslreports.com/ (insecure connection)

and it works okay on

https://www.dslreports.com/ (secure connection)

There is a change in Firefox 96 related to cookies and insecure sites. I don't understand the full details, but if you can avoid the error using the HTTPS address, then at least we have a lead on the problem.

https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Releases/96#http

Yes, that does appear to be related. https does work, although I do get a certificate warning. It wouldn't surprise me if the site wasn't configured correctly.

What is/are the exact error message(s) ?

What is/are the exact error message(s) ?

Please see screenshots in post above.

Do you possibly have old bookmarks that use the http:// protocol that you may have to cleanup ?

Sorry - yes, I did need to fix my bookmark after confirming there is a problem with http URLs.