This is normally caused by having your magnification turned on inside your browser. "Zoom out" or turn off the magnification, and you should be able to see all the chat room, including the bottom area where you type in messages.
To resolve, try one of these steps:
1. If the browser still crashes, enable "Private" or "Incognito" mode in your browser to temporarily disable all add-ons.
2. Install a more modern browser, such as Google Chrome or Firefox. Both offer exceptional performance and are more up to date.