Open Tools/Options/Advanced/General/Config. editor, right-click the preference mailnews.wraplength, Modify, and change it from the default 72. A value of 0 (zero) wraps to the window width. This applies to the wrapping of plain text messages in the message composer.

Thanks for the suggestion. I did that (config showed the value as already modified to 70). I changed it to 80, closed and re-opened Thunderbird, verified that the value was now 80, and began to compose a message with some sample text. No change; it wrapped at 40, as the screen snip shows.

However, I just set the value to zero and it does seem to fill the screen width now before wrapping; that is at least a good temporary solution.

I can confirm that TB now wraps after about 40 characters, although I have all the default settings and set to 72.

This is on Fedora 31 - Thunderbird 68.5.0 (64-bit)

I tried with all the Add-Ons disabled (just in case), but still no luck, as can be seen by the attached screenshot.

So based on:

https://bugzilla.mozilla.org/show_bug.cgi?id=853834#c1

The text is actually not wrapped after 40 characters - technically as in inserting newline characters. Rather it's just wrapped visually.

This is due to:

"If you set a minimum font size to something larger than the monospace font, wrapping is broken. Seems the line length calculation is solely based on the monospace font size (in plain text mode), not the effective font size."

I had the minimum size set to something larger (17) than the monospace font (12). Setting monospace font to 17 (as the minimum size) fixed the issue.

Thanks! Yes, I discovered that too. Setting the value to zero for display purposes while composing the text works for me.

Text wrapping is working for me but not at the line length I want.

I have set the monospace font to be larger than the minimum font size.

The text wraps to the window size which is about 93 characters per line (including spaces). I have set mailnews.wraplength to 65 instead of the default 72 but it makes no difference. See Image 1 - Wrap length isn't what I set.png

Image 2 shows a very unsatisfactory way to make the line shorter.

I want the line shorter for two reasons: 1. I am a speed reader - I read down the centre of a body of text, without moving my head or my eyes from side to side. And 2. Line length is one of the two essential criteria that make text readable for people with normal vision.

How can I get the line length to be what mailnews.wraplength is set at?

I hope you can help.

Text wrapping is working for me but not at the line length I want. I have set the monospace font to be larger than the minimum font size.

Isn't that exactly why the wrapping is broken, according to the previous post?

Sorry, but no.

The previous post said "If you set a minimum font size to something larger than the monospace font, wrapping is broken." I have always had the minimum font size smaller than the monospace font, ie as I said above " I have set the monospace font to be larger than the minimum font size."

My font wrapping isn't broken. Broken means the lines go on and on forever to the right.

The problem I am having with Thunderbird is to do with WHERE the lines wrap, ie how many characters there are in a wrapped line.

I want a line length of 65 characters (or even 72 would be nice). I want the line length that I have set using mailnews.wraplength in Config Editor.

I don't want a line length defined by the width of the screen window.

Here is what I suggest: create a new profile from Help/About TB, about:profiles, add an account, and don't change any settings except set mailnews.wraplength to your desired value, 65. If you insist on changing any other fonts or settings, beware that it may affect the wrap width already set, so at least you will know which settings have the effect of negating your wrap setting.

See attached screenprints of emails.

The mailnews.wraplength pref. applies to plain text mail. If your default format is html (or plain text) hold Shift when you click Write or Reply to switch to the other format, plain text (or html).