not able to play module 4 of selenium course showing errorwe cannot add webex extension

Change Browser, I am using 62.0.3 (64-bit and have no issue

Try this
1) Download, install webex removal tool and remove webex completely
https://collaborationhelp.cisco.com/article/en-us/WBX000026378
2) Restart PC
3) Do this setting in IE
Internet Explorer >> More options > Advanced Tab > Enable TLS1.2
Then try to play videos in Mozilla/IE
4) Try to play in mozilla. It will ask to download exe. Please download and install webex exe for mozilla and then player will launch in 2 min
5) For chrome, please install the webex exe from following link and then try to play
https://chrome.google.com/webstore/detail/cisco-webex-extension/jlhmfgmfgeifomenelglieieghnjghma/