you see the -- are actually part of the email standards. Microsoft chose to ignore the standard and now everyone thinks the Microsoft way is the correct way. It is not.

Removing the -- makes a mockery of email archival software that removed signatures as not required, or stored them somewhere else, or strips them from replies because he email does not need another 20 social media images.

Now see this solved question. https://support.mozilla.org/en-US/questions/1019583

Well I don't want it as a signature in that way. All I want is a default text like "kind regarts,\n<name>" but as regular part of the mail. I hoped the signature feature could do this for me. Is there an addon then that can do this?

Just follow the information at the link to set up your preferences to do as you want. If you are using version 78*, then the 'config Editor' button is located here: Menu app icon > Options > General Scroll to the very bottom to locate the 'Config Editor' button.

Well I don't want it as a signature in that way. All I want is a default text like "kind regarts,\n<name>" but as regular part of the mail. I hoped the signature feature could do this for me. Is there an addon then that can do this?

You could create a template with a default text section, or use Quicktext to insert it as needed.