Rated 5 out of 5 stars

Just what I was looking for. 2 questions though: What are the advantages as compared to Quicktext? And how does one insert and save a signature in jpg? The instruction for pictures under the i-link doesn't work.

Quicktext is much more powerful, the only advantage of StandardTexter: it's simple.
The instruction for pictures should work - please write an e-mail to k-l-p@gmx.de with the details of your problem and I will help you.

Rated 5 out of 5 stars

While editing, can't copy or cut anything. Paste works as expected.

Update: C-E responded quickly with a work-around. Tbird is the culprit. Thanks.

This review is for a previous version of the add-on (1.0.2).  This user has a previous review of this add-on.

Sorry, this is a bug in Thunderbird, see
https://bugzilla.mozilla.org/show_bug.cgi?id=1692327
I cannot do anything here.

Only the keyboard command Ctrl+X for cut seems to work.
As a workaround for copy, you can do Ctrl+X followed by Ctrl+V.

Rated 5 out of 5 stars

El único que me permite insertar texto y firmas en cualquier parte del correo, los otros complementos la insertan en cualquier parte

This review is for a previous version of the add-on (0.61). 

Rated 5 out of 5 stars

Does not work in the latest version of Thunderbird 78.4.0, since the option to add text is missing when you go to 'Tools' - 'Add-on Options'.

Thanks for the feedback. It indeed works as described.

This review is for a previous version of the add-on (0.55). 

This was a change in Thunderbird (on which I has no influence ... I don't know why this was changed ...). Now you have to go to 'Tools' - 'Add-ons' - find the entry 'Standardtexter' - click on the 3 points on the right side - choose 'Options'.

Rated 4 out of 5 stars

works fine... but the text is always inserted at the beginning of the message. Nevertheless, into several situations, it would be useful if the inserting is made at the cursor location (as for inserting a matched civility at the end of a message, for example).

This review is for a previous version of the add-on (0.55). 

I absolutely agree - maybe I will be able to introduce this functionality (insert the text at the cursor position) in a later version of the Add-on.
Edit: The version 1.0.2 now includes the possibility to insert the text at the end of the message or at the cursor location.