It looks to me as if the SO favicon just changed to some weird red and blue thing with the text "jB". Did anyone else notice this? And what does it stand for?
That "red and blue thing with the text jB" sounds a lot like JetBrains' favicon:
Is that what you are seeing?
The SO favicon (http://sstatic.net/so/favicon.ico) is the same as it has always been for me. This is the one linked to in the source of the SO pages.