does it work again after you restart Thunderbird? Is it only with messages from a particular sender? Some email clients use an apple line feed that does not play well in Thunderbird or instance.

No, it's ok coming from others, it's only when I try to compose a letter. Shutting it down does not help. Those to whom i write say it's not doing that for them, the messages read normally. The message body of the letter fills the entire 17 inch screen and when I type it goes to the very end of the monitor. It's the strangest thing I ever saw.

The message body of the letter fills the entire 17 inch screen and when I type it goes to the very end of the monitor. It's the strangest thing I ever saw.

That is how it has always worked for me. lines wrap when there is a need, not at some set number of characters like used to happen when you set up a typewriter. Or after 80 columns like used to happen with the old IBM 3270 monitors

It may be that in the past you have composed mail in plain text (hold shift when you click to write / reply and see if that is what you are expecting. I do not recommend the use of plain text these days as so few mail clients can handle it gracefully.

I think I may have used plain text in the past but when I hold shift all I get all caps and it still goes to the end of the screen without stopping. I have to use a scroll bar to even see the end to see if I have any spelling mistakes. I appreciate your attempts to help.

Tools/Options/Advanced/General/Config. editor, check the value of mailnews.wraplength. Setting it to 0 should make composed plain text messages wrap to the window width. Otherwise, see if the same wrapping issue occurs in safe mode (hold Shift when you launch TB).

Thank you for your help.

I set it to 0 and I opened it with shift but it still does the same thing. The first line sort of wraps, at about 13 inches, but the second and the rest of them run all the way out of sight.

I keep thinking there's something about this giant display which is wrong. The scroll bar on the bottom literally runs out of sight if you try to see where the line has ended.

Is there some way to open a new Thunderbird and use it without losing all my saved folders and emails in them in the current one which I need?

You could create a new profile, add an account, and see if the wrapping issue disappears. The original profile is untouched and can be opened if necessary, or if the new profile works properly, mail and other data can be transferred from the old to the new profile. Help/Troubleshooting, about:profiles, to create and manage profiles.

Thank you for that information, I did not know that. I will try it.