评分5星,满分5星

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.

这个评论是针对附加组件的一个早期版本的(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'.

评分4星,满分5星

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).

这个评论是针对附加组件的一个早期版本的(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.