I use windows 8, and for life of me can not get ducking to work properly.

I am trying to get Teamspeak to reduce volume on Pandora Radio when others talk. Now I found installed the addon for it, but for life of me I cannot get it to reduce volume of Pandora when using Firefox or Google Chrome.

I've troubleshooted with others and we couldn't find a solution so I ask TS community for possible answers.