I'm often amazed by how many screenshots of Firefox include a critical update icon. A red disc in the top-right of the browser window means there is a critical update to Firefox available and that you should upgrade immediately.
Yes, it's crap UI, which is why it's gone in Deer Park - there's a nice, big “You need to update Firefox now” dialogue instead. But I'm still surprised by how many people completely dismiss it. I assume they can see it's there; is nobody interested in finding out what it means? It only requires pointing at it.
Maybe the icon should have had a large label reading “Your computer may be commandeered by randomers. Click here if you'd prefer it not to be.”