How To Make Thunderbird Compose Mail With “Body Text” As Default

1. Start a new message
2. Select the "Format Text" tab
3. Make sure the cursor is in the body of the text (click somewhere in the body)
4. Choose the style you want under the "Styles" section
5. Click the "Change Styles" button in the "Styles" section
6. Click "Set as Default"

Your selection should now be the default under all new emails. As well, if you select the formatting settings you want (using the "Paragraph" section), you can save your settings to a new style by clicking [ Change Styles > Style Set > Save as Quick Style Set ], then save that newly created style as your default.

Hope this helps!

I have found that to set the default to "Paragraph" or "Body Text", you need to navigate from the main menu:

Tools->Options->"Composition" region -> "General" tab

In the HTML section, find the option for "When using paragraph format, the enter key creates a new paragraph"

Select that option if you want "Paragraph" as the default. Deselect that option if you want "Body Text" as the default.

I am using Beta version 45.0 of Thunderbird