It is a bit rare, but still happens. Sometimes the answer I'm looking for in google doesn't appear to be in stackoverflow site, but rather in the quora.com site.
And this is annoying, because quora asks you to follow topics, and asks that with an intrusive method: a layer with opacity all over the background that obscures the answers you're looking for. Every time I had to open firebug or the developer console in order to delete html nodes on the fly.
So I wrote a super simple greasemonkey script that removes this stupid layers when the window content is loaded. Here it is: