issue with "open in a separate window" button

Hi, I have Zimbra 8.0.7 (including the heartbleed patch) with ZeXtras 1.8.16. Chat module seems to work fine except that when you click on the "open in a separate window" button, you do in fact get a separate window that looks like it's the right size, but it's blank, and (at least in Firefox anyway) the mouse cursor turns into a red circle with a line through it when hovering over the window. Any suggestions?