This question is an exact duplicate of:
I use Firefox with the "Disconnect" add-on which has the feature to block e.g. content from Facebook etc.
Some of the SE users' icons are from Facebook so if we block that, these icons do not load and are invisible, which is acceptable though.
However, during Winter Bash, there are hats added to the icons. Unfortunately, if the original icon is blocked from loading, the hat just gets placed in the top left corner of the visible screen:
This is a bug, although it's only a minor one because it probably doesn't affect too many users. I would like to suggest to hide the hat if the icon did not load (yet or at all) instead of placing it in the top left corner.
Related issue (from chat, not main sites): Hat icon appearing in top left of chat room, not over user picture