It would be helpful if there's other info such as the url of the pop-up, or screenshot of it.
Also, you might want to run a spybot scan just for making sure, and this issue has been notified to the site owner [Noejeko].
Also, probably it may come from ijji website itself, as you mentioned
Everytime I open Firefox I open Ijji, then YouTube, then here.
You might want to send them email about this, too.