Cannot reach referenced URL's

See this article for some possible solutions:

https://support.mozilla.org/en-US/kb/hyperlinks-in-messages-not-working

The most likely is to reset your default web browser in your operating system (in Windows, see Settings | Default Apps.) If it appears to be already set correctly, change it to another browser temporarily, then change it back to your preferred.

I changed the default web browser to Google Chrome and was able to see the URL's referenced in my emails. However, when I changed the default web browser to Firefox, the URL image did not appear. Just a brief lighting of the top tool bar. I previously reset Firefox successfully and I can view content if I plug in a URL into the Firefox browser window. Seems there is a problem between Thunderbird and Firefox in this case.

It could be something peculiar about your system because it works as expected for me with Windows 7 (both 32- and -64bit), Thunderbird 115.18.0, and Firefox 115.39.0esr.

If I had to point a finger, it would be at the aftereffects of your trojan cleanup.

Some other things to try:

- Restart Thunderbird in Troubleshoot Mode (see Help | Troubleshoot Mode). This is not a permanent solution but might provide a clue.

- Reinstall both Firefox and Thunderbird. The old Thunderbird installer can be found here:

https://releases.mozilla.org/pub/thunderbird/releases/115.18.0/

and Firefox here:

https://releases.mozilla.org/pub/firefox/releases/115.39.0esr/

If those fail to remedy the issue, perhaps creating a new Profile as a test.

I did not do anything since my last posting, but again I cannot access URL's referenced in Thunderbird email handler. When I try to access a file, I get an error message. Suggested fix with checking SSL and TSL shows nothing bad

I'm sorry, but I can think of no more suggestions. You seem to have something on your computer that is resetting Windows' preferences, but without having hands on the machine, there's no way I could know what that is.

I don't know what you're referring to by "suggested fix with checking SSL and TSL".

If I set Google chrome as my default program in the control panel, clicking on an embedded URL will display properly in a Google window. If I then change the default program to Firefox, nothing appears in a Firefox window. What has this to do with Windows preferences?

After reloading Firefox, it started to work as the default browser. Clicking on URL's in an email now can be displayed in Firefox.

I did not do anything since my last posting, but again I cannot access URL's referenced in Thunderbird email handler. When I try to access a file, I get an error message. Suggested fix with checking SSL and TSL shows nothing bad

What is the error message. Verbatim please.

My guess is your antivirus product of choice is not Microsoft Defender and it is out of control. Generally when messages about SSL/TLS appear it is because your antivirus is hacking your encrypted connections with an unrecognized self signed certificate. Somehow Defender can do it's job without that for of hacking. But it is common for paid product.