In earlier versions of Thunderbird, the Enter key inserted a line break rather than creating a new paragraph. Now Enter creates a new paragraph and '''Shift+Enter''' inserts a break between lines in the same paragraph. This was changed to conform with the way most HTML editors work now. If you prefer the old way, there is a checkbox for that in the Options/Preferences dialog: Windows: "3-bar" menu button (or Tools menu) > Options Mac: "3-bar" menu button (or Thunderbird menu) > Preferences At the top click Composition, then below that, the General mini-tab At the bottom of the HTML section, uncheck the box next to "When using paragraph format, the enter key creates a new paragraph" and click OK to save the change. Success? Some screen shots other users have posted in case a picture is worth more than the above words: https://support.cdn.mozilla.net/media/uploads/images/2016-05-02-22-59-34-93ae69.png https://support.cdn.mozilla.net/media/uploads/images/2016-04-26-19-35-55-46d3f6.png