How to fix SSL_ERROR_ACCESS_DENIED_ALERT on server side?

Question

Browsers

About once a month I receive complaints from customers that the site does not open.
After long negotiations, we managed to get a screenshot from one of them)

As it turned out, Firefox wrote to the client - SSL_ERROR_ACCESS_DENIED_ALERT

Of the reasons, we managed to google dr.Web and the browser itself, but all these problems are on the client (browser) side. But, all clients with dr.web cannot be caught) I would like to somehow solve the problem on the side of the site.

What can cause such an error and how to overcome it? Failed to play. The certificate is from Let's Encrypt

Answer 1

https://support.drweb.ru/new/urlfilter/

Answer 2

Faced similar behavior with Avast and Kaspersky. It is necessary to disable SSL checking on antiviruses.
Ears with legs grow because of the substitution of the certificate by antiviruses, it was like that. When active, the antivirus wants to scan Internet pages, but if they are encrypted, then it will not be able to do this. There are two ways out: make an SSL micro-proxy server for the antivirus and / or implement an extension for the browser.
My opinion: These are not your problems, but, for example, greedy people who install broken antiviruses)))
Offer clients to whitelist your site.

solve the problem on the side of the site

How to check the client for the possibility of https connection. For example, through an iframe. Insert https into http. If the return is not what is needed, then we draw the http page that the client needs to update the antivirus. But there you have to pervert with Headers, it’s easier to score on such clients. ))) Why do you have such hemorrhoids? )))
A more difficult situation is a stolen Widows)))