WebEx is invaluable for professionals - it's well done (you CAN share anything, actually!) and is one of the few using the standard web ports, which eliminates the need for special IT permissions always impossible to get in large corporations. I am a heavy user of it, both hosting and joining meetings very regularly.
For a long time, the add-on only worked in the 32-bit Firefox (while my regular browser is the 64-bit Waterfox), and even worse, it stopped working completely in the recent Firefox versions...

But I have just installed the BRAND NEW v.1.0.1 (you may need to go to the Version Information section to get it) and not only does it work in the latest Firefox, but ALSO in Waterfox 50.0.2! Good job there... at last!