Thunderbird: How to put your signature at the top of the reply

Since I'm using Thunderbird as my email client (I have to manage several email accounts, business and private, and Thunderbird is the best tool in my view to achieve that) I want to customize it to best achieve my needs of course.

An email reply with quoted emails arranges the answer like this.

my handwritten reply
...
the quoted email
On .... xyz wrote:

Dear Andreas,
...
my signature file
Best regards
Andreas

What I actually wanted was a different order: the signature should be on top of the original email like this.

my handwritten reply
...
my signature file
Best regards
Andreas
the quoted email
On .... xyz wrote:

Dear Andreas,
...

In order to achieve that I had to adapt two settings.

First of all there is a general setting maintained in Thunderbird's config file. One can change that in various ways (depending on OS) and on my Mac I'll get to it via Thunderbird -> Preferences -> Advanced and the button Config Editor ... which opens the config file. There is a setting mail.identity.default.sig_bottom which is true by default and double clicking will turn it to false.
This is a setting for all accounts but unfortunately it does not yet achieve the desired result. The signature still sits at the bottom of the quoted email. The change basically was just an enabler to shift the signature file.

Now comes the fine tuning of the accounts. You can decide for each account where to put the signature file and this is done by ticking a few boxes and making the right selections.
Pick the email account and go to View settings for this account and choose Composition & Addressing. Aside from ticking the appropriate boxes the most important change was to choose where to put the signature 'below my reply (above the quote).

Of course I did not invent this answer but rather than having to search for it in Mozilla forums again and again (in case I forget) I put it down here as much for my own good as for the reader's who quickly stumbles upon it in a web search.