Stories and ads in USA TODAY Daily Briefing are duplicated in Thunderbird

Can you show a screen shot (redact your email address)? That might clarify what you mean by "duplicating".

Do you have Thunderbird set to automatically show remote content? This option is found at <Settings | Privacy & Security | Mail Content | Allow remote content in messages>?

Does the email have a "Show in browser" option? How does the message look in a browser?

Without seeing the actual source code of the email my guesses are...

Thunderbird can only render the content of what's actually in the message, and unfortunately, many emails contain invalid web (HTML) code or formatting. Some readers are more strict or lax than others at glossing over those errors - maybe Thunderbird is one of strict ones.

Many or most HTML emails also include a plain-text version, and code in the email separates the two versions. It could be that the separator is incorrect and Thunderbird can't distinguish between the two and so displays them as one.

This is all a long-winded way to say that there may not be anything you can do. But try switching the message view between "Original HTML", "Plain HTML" and "Plain Text" and see if you like the appearance better. This setting is found at menu option <View | Message body as>. If the menu is hidden, press <Alt> or <F10> to reveal it.

I am grateful for your thoughts. I do have Thunderbird set to automatically show remote content. And when I "show in browser," the email shows properly with no duplicated ads and stories (also the problem does not show up on the email that comes to my iPhone), which tells me it's a Thunderbird issue. I also tried switching between Original HTML and Simple HTML and Plain Text, but nothing changed. Yes, I do realize there may be nothing I can do, but at this point I'm still trying to find the solution. Lin, you are very bright and I thank you for your time!