Not sure if this is just me, or a problem with this specific ad - there's an animated ad for Air NZ that for the last few days has been popping up above the quick reply box, but it's wider than the box it seems it should sit in, and overlaps ads to the right of it.
I presume it's unrelated to moving to HTTPS, but maybe not??
Also, same ad seems to cause processor usage to spike and the fans to go nuts.
Firefox / OSX
EDIT: As soon as I posted, the ad was replaced with a similar one for NZ Army showing the same issues, so I guess it's not that specific ad that's a problem!