In my address bar, on the left of the star, there is an option Snapback: [Empty] for every site. I haven't seen this before and I don't have the Snapback plugin. Doesn't anyone know where it may have come from and what it does?

I recently upgraded to 3.5.6 on Ubuntu, and may have had some plugins upgraded, but not sure which. I have a ridiculous number of plugins on this comp otherwise I could just try disabling them one at a time.