Since you listed no URL or the problem site how would one expect anyone to know what is happening or how to replicate the issue? User have already mention they use it on Win7 and Win8 so not sure what your last comment has to do with Firefox if it runs on previous O/S already.

The most crucial site is https://americanancestors.org. The error window is:

It opens just fine on firefox for me. So did you verify if this problem was there in Private Mode window browsing as well?

This article may help.

https://appuals.com/fix-error-code-15-this-request-was-blocked-by-the-security-rules/

So did you verify if this problem was there in Private Mode window browsing as well?

I did.

This article may help.

I have tried everything in that article except using a VPN, which I cannot afford to pay for. As I stated earlier this is a browser-specific problem - it does not occur in Edge or Opera.

It opens just fine on firefox for me.

I apparently did not state the problem clearly - I can access the site but cannot log into it - I get the error agter the site processes my login. I have to use Edge or Opera to log in.

Until another user of the same site tries to login with Firefox that is the only way to know if that is a Browser or Addon issue or site issue with the Browser.

Try troubleshooting.

https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems (also deals with hardware acceleration)

You can check for issues with Total Cookie Protection.

• https://support.mozilla.org/en-US/kb/total-cookie-protection-and-website-breakage-faq
• https://support.mozilla.org/en-US/kb/introducing-total-cookie-protection-standard-mode