After all: Stationery is working on OSX with TB 3.1.6 Rated 3 out of 5 stars
I'd like to correct my negative judgement from the other day:
Stationery 0.6.1 is working on my Mac-OSX 10.6.4 (Snow Leopard, intel) within my Thunderbird 3.1.6.
From Arivald's kindly answer on my alleged failure indication I learned how to use it - and how to create my own stationery/templates.
Because this might be useful to others interested in using and costomizing some existing stationery in TB - or creating there own ones - I report some passages of his reply:
The problem is related to fact that Stationery uses only HMTL files as templates. Currently there is no support for loading templates from Templates folder.
You can use HTML Source view (best when having installed Stationary add-on) to create HMTL file.
Make template in TB.
Switch to HTML source page (view), select all text and copy it to clipboard.
Open TextEdit or any other text editor (but NOT text processor like MS Word!), Paste from clipboard, and save file with "html" extension.
Now You can load this newly created HTML file in Stationery. E. g. by chosing Create Messages / Answer / Forward and pointing to the folder with the (stationery/template) html file you created (or which one you have from elsewhere, but must be html file). This loads this file in TB.
So you can write your message in it, address it etc. and send it.
Remaining critic is, that this is not described in a way for me intelligble in the short add-on description on this site. A link to a tutorial would be helpful. - Thanks to Arivald!