Created attachment 8591346 [details] Screenshot 2015-04-12 07.43.03.png See screenshot. A big panel with only two buttons, unlabeled. Looks buggy to me.
That is very strange indeed, given the icons are embedded in that page as data urls (you should see 6 buttons, I'll attach the image). I'm not able to reproduce this. If it's consistently reproducible for you, I'd like to figure out what is happening. FWIW That panel only appears to early-beta so it's not terribly urgent, and am waiting on a new design.
Created attachment 8591880 [details] Screen Shot 2015-04-13 at 1.31.27 PM.png this is what it should look like.
I see this consistently on my long-term Nightly heavy-use profile, even after relaunch. I'd use the Browser Toolbox to inspect it, but of course the tray disappears the minute I click anything, and there's no keyboard shortcut.
(I don't see this on one of my testing profiles.) Anything in particular I can do to pin this down for you?
The culprit is AdBlock Plus. 22.214.171.12430 is the version I'm running. I'm using Fanboy's Social Blocking List as a filter subscription.
It's odd that blocks the icons (which are data urls) when the page is loaded in the panel, but it doesn't when it's loaded in a tab. Not sure what to think of that. It may be indiscriminately blocking the image in the page if it has certain alt tags.