Rated 4 out of 5 stars

I had the same problem: it stopped working automatically. So I uninstalled 1.6.2, manually *removed* all "signatureswitch" entries from prefs.js in my profile, then installed 1.6.3 from the developer's Web site. It works again. I'm still taking off a star because it's not as responsive as I would like: I have to go back and click the recipient's address to get the signature to switch automatically.

This review is for a previous version of the add-on (1.6.3).