That's weird...

Thank you for sharing your add-on info, listing Avast. If you haven't already, could you try disabling the Avast WebShield? That is a "man in the middle" of your connection to websites. Even if you have a highly secure connection to the WebShield, Avast controls the connection to the website. So I'd like to rule out that possibility.

This article has information on tracking that down in Avast's controls: How to troubleshoot security error codes on secure websites.

Disabled WebShield completely. Did not change result. The complete 'message' I am getting when I click on the Amazon link in an email is as follows:

The browser or mobile device you use to access the internet does not support modern security standards that Amazon and others use to protect customers. To complete the entry of your payment information, please upgrade or use a different browser or mobile device to ensure that your experience on Amazon will be uninterrupted.

I did further troubleshooting. There are five links in the Amazon email. I tried them all. The 'error message' does not come up if I click on the link for the book that is 'featured' in the email, but does for the 4 additional books that are under the "Recommended for You" heading. Same occurred for several previous Amazon recommendation emails that I went back to and tried again. Perhaps problem is Amazon's

Hmm, do you notice any difference in how the successful and unsuccessful links are routed? Commercial emails usually have heavy tracking on links and you may be redirected over multiple servers before landing on the ultimate destination page. Possibly a privacy-related feature or add-on is modifying the information provided by Firefox to some of those pages, causing the message. But that's just a guess.

Boot the computer in Windows Safe Mode with network support (press F8 on the boot screen or hold down the Shift key) to see if that has effect.

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/
• http://www.7tutorials.com/4-ways-boot-safe-mode-windows-10

Note that this is probably about supporting TLS 1.3.

You can check your browser.

• https://www.ssllabs.com/ssltest/viewMyClient.html

Actually it may be about using a browser that supports TLS 1.2 as Paypal and Ebay was all about that in June and July before August date.

Firefox has supported TLS 1.2 by default since 27.0 and TLS 1.3 by default since 60.0