Rated 5 out of 5 stars

Great Extension! Before some updates it was possible to load the signature from an .html file, can you add this again to the extension?
Changing the .html file would change the signature. This way I was able to change the signature of everyone in my company without having to change anything on their thunderbird.

This review is for a previous version of the add-on (2.6.1). 

The latest version of Signature Switch (2.7.0) can load content from a native application via "native messaging".
That way you could distribute a "company wide" (and possibly dynamic) signature.