Apparently there is a problem with WebEx and Windows 8. I believe it’s more of an IE 10 issue but firefox doesn’t work either. If you have webex and want to use Windows 8, the only way I know how to do this is through Chrome using incognito. Click the right side (with three lines), open new incognito windows and copy and paste the webex link. You’ll probably have to OK a few java warnings but it does work.
Hopefully WebEx will be updated to support Windows 8 and if you have this issue, I hope this helps.