Computer related problem

I was browsing today on a common gaming site I visit that utilizes the website invisionfree as the base for the forums. They have a chatbox on the top, but today, not like other days, it did not work. Instead (because I have a firefox) I received a pop up prompting me to download the application/ octet-stream from: http://www4.cbox.ws

Obviously without it, the chatbox doesn't work. But I don't know how to run it, as the browser asks you which program to use (I don't know why it suddenly did this), and I have no idea what to tell it to use. I was previously using AdBlock Plus to block some annoying music if that helps.