There are many reasons that a site might not support mobile browsers, from add-on support to screen resolution. I'm not familiar with the reasons of the Webex site. Do other mobile browsers work with the site?

yes it works with Chrome

Desktop version of Firefox 47.0.1on windows 7 works fine also

WebEx's system requirements document doesn't even mention Android, so I think I'll stop researching that: https://help.webex.com/docs/DOC-4748

Sounds like you can do your mobile meetings either in Chrome or in the Cisco WebEx app: https://play.google.com/store/apps/details?id=com.cisco.webex.meetings (I think the app intercepts meeting links after you install it)