Is there a way to stop the chatbox from popping up
To prevent Chat from popping up, you need to change your on-line chat status.
First, close pop-up; click on dialog balloons at the bottom right of the screen, on the black tab, next to "Chat(NN)" label. This will bring up a list of all participants with you at the top. Change your status to "Off-line" to turn off the tab and pop-up, or "Busy" to stop only the pop-up.
If you want to turn it back on some day...
You should see a semi-transparent dialog balloon icon in the lower right corner; clicking on it will restore the Chat tab and switch your status to "Available". The icon does not show up when you are in the Forum, and perhaps in some other areas of the site. Reload the page; if it is still not there, go to another section.
Thank you for your explanation!