How do I get WebEx fully working with Ubuntu 12.04?
For those of you who are still struggling with this...
I have tried many steps and recommendations from other posts and nothing has worked for me in Firefox (Ubuntu 16.04 64bit).
The only way for me to get Webex fully working was to install VirtualBox and then install Windows as a virtual OS. Yes, it's a bit inconvenient to run a virtual OS each time you need Webex, but you can be 100% certain that it will work perfectly (voice, video, screen sharing).
Good luck!