Prof. Antoniou Rated 4 out of 5 stars
I have found your Signature Switch Add-on quite useful. It would have been a 5-star review if only the signature would appear immediately below the user's reply independently of where the reply is placed, at the top, spliced in, or at the bottom. That took away one star.
As for the separator, namely, the dashes, before the signature, I delete it anyway and include my own separator. I would suggest deletion. And that much has been said by several other Thunderbird users.
And now for something completely different. I was using Add-on QuickText before for signatures and also for templates whereby you create standard letters as templates which could include their specific signatures. Alas, QuickText became disfunctional on the most recent Thunderbird update and when I checked a day or two ago, it was still disfunctional. So I switched, well you guessed it, to Signature Switch. And before too long I realized the your Add-on can be used to provide templates as well, just like QuickText used to do.
Facilitating the insertion of the user's signature (along with a possible template) at the top, spliced in, or at the bottom of the received message would make your Add-on as useful as QuickText used to be and that would restore my ranking of Signature Switch to 5 very good stars.
It should be fairly simple to do and I urge you to do it. Many of us Thunderbird users will be indebted to you.