That is a problem with your e-mail provider. Many have size limits. Check the mail. Is there a see message in browser link? It may be near the top.

It says:

Truncated!

This message exceeded the Maximum Message Size set in Account Settings, so we have only downloaded the first few lines from the mail server.

Download the rest of the message.

Is this a question about Thunderbird?

If that is the case then we can move the question over to Thunderbird support.

This IS a Firefox problem. Firefox is my email provider. If I can go to them maybe that will help. How do I get there?

Firefox is only a web browser. look at your e-mail address. The part after @ is your provider.

Hello,

In order to better assist you with your issue please provide us with a screenshot. If you need help to create a screenshot, please see How do I create a screenshot of my problem?

Once you've done this, attach the saved screenshot file to your forum post by clicking the Browse... button below the Post your reply box. This will help us to visualize the problem.

Thank you!