Some problems occur when your Internet security program was set to trust the previous version of Firefox, but no longer recognizes your updated version as trusted. Now how to fix the problem: To allow Firefox to connect to the Internet again;

• Make sure your Internet security software is up-to-date (i.e. you are running the latest version).
• Remove Firefox from your program's list of trusted or recognized programs. For detailed instructions, see

Configure firewalls so that Firefox can access the Internet. {web link}

Thanks, Fred--but my issue remains. The site I've been trying to access is marklets.com, and the fix to which you linked didn't help.

Server not found

Firefox can’t find the server at www.marklets.com.

http://marklet.com/ does work

Please explain the problem in detail. What happens? What is/are the exact error message(s) ?

The site is marklets.com.

What happens? I see a standard Firefox error page [below]

What is/are the exact error message(s)? Hmm. We’re having trouble finding that site. We can’t connect to the server at www.marklets.com. If that address is correct, here are three other things you can try: Try again later. Check your network connection. If you are connected but behind a firewall, check that Firefox has permission to access the Web.

Did you try the link I posted?

There is security software like Avast, Kaspersky, BitDefender and ESET that intercept secure connection certificates and send their own.

https://support.mozilla.org/en-US/kb/firefox-cant-load-websites-other-browsers-can

https://support.mozilla.org/en-US/kb/firefox-and-other-browsers-cant-load-websites

https://support.mozilla.org/en-US/kb/secure-connection-failed-error-message

https://support.mozilla.org/en-US/kb/connection-untrusted-error-message

Websites don't load - troubleshoot and fix error messages

http://kb.mozillazine.org/Error_loading_websites

What do the security warning codes mean

Fred, I thank you for your interest, but you don't seem to be paying much attention to what I've said here. Your most recent question, for example, was previously answered clearly, as had been your questions in the post preceding that one (and which I answered again in my reply). As I told you, your original link was no help. Under these circumstances I don't have time to check out the seven new links you've posted.

I called for more help.

Looks that the site is gone.

• http://www.moreofit.com/similar-to/marklets.com/Top_10_Sites_Like_Marklets/
• https://www.google.com/search?sa=N&num=100&q=marklets.com

Thanks, cor-el. Checking on web.archive.org, it seems you're correct.