Chatroom memory usage?

When chatting for a length of time (> 10 mins) an Internet Explorer 8 user gets increased response times and irratic cursor/slow feedback in the chat box. This is repeatable, but seems to function fine on a Chrome or Firefox client. If the user exits the chatroom and re-enters the issue is cleared temporarily, so there is a work-around but not a solution. Memory usage seems to be the issue, with an ever-increasing memory footprint.