Keep getting this pop up http://macassists.co/chatsupport/

If this is happening when using Safari then shut down Safari then while pressing and holding the shift key launch Safari. This will start Safari in a clean state. If you are not using Safari when this happens please provide details about when the pop up occurs.

more words for what Bob said:

Quit Safari,

Start Safari while holding the Shift key: Safari starts without the pop up,

Open Safari Preferences->Advanced: check the underneath line "show develop menu in menu bar",

In the new menu point Safari->Preferences->Develop: click "empty caches",

In Safari->Preferences->History: clear history->all history.

The popup should not return.