Which platform? Mine are still there, at least for sites I've visited semi-recently. Matter of fact I think it must be helping itself to Camino's cache, because I don't believe I've been to some of those sites in FF in the past six months.
Didn't they use to have some kind of generic favicon? Now it's just a depressing little box.
The Site Identity Button has changed to protect users from hackers trying to "spoof" legitimate looking site buttons. The site icon will still appear on bookmarks and on tabs, but not at the left end of the Location/URL bar.