It is pop up advertisement for a highly dubious dating / sex site.
If you have your browser set to block pop ups it will slow down the window loading as it is coded to load the advertisement first.
Don't know if it is on the server or on our computers.
I run malwear detectors regularly although to date the Mac has never been hacked and it found nothing.
And as it on appears on this site I assumed the web host added it.
You could try googling ( removal of FUBAR pop up add or removal of ubercpm pop ups and see what come up )
Apparently a really cutie pie called Cindy lives 500 meters from me and Wendy who wants to have fun is only 1100 meters down the road.
This is rather interesting as this computer is on a rural property , the landlords house is 800 meters away and the next nearest house is over 2.5 km away