Does it still happen in Troubleshoot Mode?

Yes, it still happens in Troubleshooting mode. Also 118.0.1 just loaded. No change, same error.

Does it still happen in a new profile? An easy way to test a new profile is to install Developer Edition and see if it happens there or refresh your existing profile.

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

You can try these steps in case of issues with webpages:

You can reload webpage(s) and bypass the cache to refresh possibly outdated or corrupted files.

• hold down the Shift key and left-click the Reload button
• press "Ctrl + F5" or press "Ctrl + Shift + R" (Windows,Linux)
• press "Command + Shift + R" (Mac)

Clear the Cache and remove the Cookies for websites that cause problems via the "3-bar" Firefox menu button (Settings).

"Remove the Cookies" for websites that cause problems:

• Settings -> Privacy & Security
  Cookies and Site Data: "Manage Data"

"Clear the Cache":

• Settings -> Privacy & Security
  Cookies and Site Data -> Clear Data -> [X] Cached Web Content -> Clear

• https://support.mozilla.org/en-US/kb/clear-cookies-and-site-data-firefox
• https://support.mozilla.org/en-US/kb/how-clear-firefox-cache

Start Firefox in Troubleshoot Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration or if userChrome.css/userContent.css is causing the problem.

• switch to the Default System theme: "3-bar" menu button or Tools -> Add-ons -> Themes
• do NOT click the "Refresh Firefox" button on the Troubleshoot Mode start window

• 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

• https://support.mozilla.org/en-US/kb/enhanced-tracking-protection-firefox-desktop
• https://support.mozilla.org/en-US/kb/smartblock-enhanced-tracking-protection
• https://support.mozilla.org/en-US/kb/trackers-and-scripts-firefox-blocks-enhanced-track

If clearing cookies doesn't help, it is possible that the cookies.sqlite file in the Firefox profile folder that stores the cookies got corrupted.

• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

• rename/remove cookies.sqlite (cookies.sqlite.old) and when present delete cookies.sqlite-shm and cookies.sqlite-wal in the Firefox profile folder with Firefox closed in case cookies.sqlite got corrupted.
• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

To ZeroKnight

Now that I have another helper, I am going to finish the path with Zeroknight so I am only working one solution at a time.

Yes, there was no error from the Walgreens site when I downloaded and used Developers Edition. Nothing seems to have been transferred from v118 of FF to the Developers Edition so I manually found the web site and entered my login manually. When I select either option that should display my prescription, they do display prescriptions without error.

So what is my next step and how do I perform it?

Thanks.

Starting with zeroknight suggestion to download the developers edition, it was clear something in the profile must be the problem. I refreshed my usual version 118 but that did not solve the problem. I then looked for items NOT changed by refresh and decided to try cookies first. In v118, I deleted the "cookies and site data" for the Walgreens web site only and that solved the problem. The same error message appears once per session but even that does not disable my prescription data which now appears whenever it should. I am always concerned about what I might lose from deleting cookies but it appears that I only lost "My Walgreens" which was easily selected again. I also have used the vaccination portion of Walgreens' site and I have not tested that but I seldom use that function unlike prescriptions which I use frequently. I expect vaccinations to work but might have lost some easy-to-replace data. BTW, I don't know what was in all those cookies. Before deleting, there were over 100 for walgreens.com. After deleting and reloading the web site, there were only a little over 70 recreated. Well, I'll never know but it is great that it works. Thank you zeroknight and thank you cor-el. Claude