I'd be willing to bet that Firefox would treat them as such, even if they returned something different. Still, those favicons should be bundled instead of making requests, IMO.

Because we can see the sum of the requests, I think it's safe to say that they are probably just images.

There's nothing to stop, say, ebay from serving PHP scripts on ICO extension, processing the request as a pageload and then ultimately returning the icon file, but for anything useful to have been gleaned, it would have generated more requests.

Either it did generate more requests and Mozilla didn't honor them (in which case, yay), or it didn't generate more requests (in which case, yay). The former would be slightly preferred as the latter doesn't prevent ebay from later changing their strategy.