[TheLoneWolfling]

The problem is that there is no difference.

Or rather: you can simulate animated gifs with dynamically setting the favicon. And as such blocking animated gifs wouldn't do anything beyond driving people to use JS to animate them instead.

So, realistically, either block both, block dynamically setting it but allow animated gifs, or keep both. But blocking animated gifs but allowing people to dynamically set it won't do much of anything.

Personally, I'm for blocking animated gifs (or rather, making it a config option), and throttling dynamically setting the favicon (like how FF already throttles background JS events). Unfortunately, given FF's push towards no options, I very much doubt it's going to happen.