Every browser handles popunders differently. Generally speaking update in 11/2013 made popunders in Chrome browser very problematic, but updates in 2/2014 resolved it but starting from 4/2014 they are nearly impossible.
You can get popups or tabunders at Github for example. I have the popunder for Chrome it cost me many thousands dollars and I would never sell it. Firefox, IE popunders still work fine.
Even below average javascript coder however can get the any code from any page and implement it.
If you talk to God, you are praying; If God talks to you, you have schizophrenia.