Try changing secure DNS over HTTPS (DoH) to "Off" or "Max Protection" and in Connection Settings change "Use system proxy settings" to "No proxy".

Does it still happen in a new profile without signing into Sync? Alternatively, you could refresh your existing profile.

Thank you for the prompt reply.

Sadly, I tried making the suggested changes to settings and created a new profile, but in all cases the results were the same.

I am reluctant to refresh my existing profile because I want to retain the customizations made to it over the years. I am no expert, but I don't understand how refreshing my existing profile could make a difference if creating a new profile would not work

You can remove all data stored in Firefox for a specific domain via "Forget About This Site" in the right-click context menu of an history entry ("History -> Show All History" or "View -> Sidebar -> History").

Using "Forget About This Site" will remove all data stored in Firefox for this domain like history and cookies and passwords and exceptions and cache, so be cautious. If you have a password or other data for that domain that you do not want to lose, make sure to backup this data or make a note.

You can't recover from this 'forget' unless you have a backup of involved files.

If you revisit a 'forgotten' website, data for that website will be saved once again.

• https://support.mozilla.org/en-US/kb/delete-browsing-search-download-history-firefox

Thank you for the reply.

However, I encountered a problem in attempting to use your suggested solution. Because FF could not connect to the site, its URL does not appear in the "Show All History" list. When I attempted to access the site the tab simply showed "Problem loading page" instead of the URL. As far as I could see, there was no way to use "Forget About This Site" for the website in question.

What security software do you use? It may not interact well with Firefox.

Thank you for your interest, Terry, but I believe that the answer is irrelevant. I have been successfully accessing this website for well over a year without any problems. It is only in the last week that the issue has arisen, and I have made no changes to my security software during this period.

You should try disabling any third-party antivirus or security software, you may need to reboot into Windows Safe Mode to stop it from interfering.

Thank you for the suggestion. Unfortunately, booting into Safe Mode produced the same undesired result.

Try changing your IP address by using a VPN or your phone's internet via Wi-Fi hotspot.

Thank you. Using the VPN on my Windows PC to change the IP address produces the same undesired result.

I do have alternate means of accessing that website, although I would prefer FF to be working as I believe it should. Chrome for Windows on my PC works, as does the Android app on my Samsung Galaxy S8 tablet. Curiously, Chrome for Android on the S8 tablet does not work, returning the error message ERR-TOO MANY-REDIRECTS.

Try using the User Agent Switcher extension to spoof as the latest Firefox 120 version on Windows 10.

Thank you, but I think I will leave well enough alone. I am not comfortable trying this type of extension that a significant number have reported as either causing problems or not working. I spent a fair bit of time restoring my system to its state before trying some of the suggested solutions here and elsewhere. For the time being at least, I can live with the workarounds available to me. It is probably time for me to consider upgrading from Windows 8.1, given how it is no longer supported by a number of entities.

You can check the Network Monitor to see if there is some clue of why the server complains.

• https://firefox-source-docs.mozilla.org/devtools-user/network_monitor/
• https://firefox-source-docs.mozilla.org/devtools-user/web_console/

If necessary use "Ctrl+F5" or "Ctrl+Shift+R" (Mac: Command+Shift+R) to reload the page and bypass the cache to generate a fresh log.

I am both baffled and delighted. I now have access to the website again.

I have no idea why access has been restored. The only thing I did at my end was access the Network Monitor and Web Console as suggested by cor-el. As I did not know what to look for, I really did not analyze the content. However, when I entered the URL after doing so, I was connected.

Thank you all very much for your suggestions. I really appreciate your assistance. I hope that issue has been resolved permanently.

Best regards, Allan