Why do you need a extension for that? Wouldn't it be enough for the client app to register a custom URL scheme handler and their website using that custom URL scheme to open the client?
It also doesn't inspire confidence that this is the screenshot of the Chrome Extension they give users to encourage them to use the extension: http://imgur.com/a/Rsy3H
(For those who don't want to click, the screenshot showing the install has the rating from the Chrome Webstore, which is currently at 2 stars)
I mean, I applaud the honesty of showing us what users have rated it, but it just seems kind of sloppy to me.
Currently it's a maze of dialogs only technical people are able to navigate successfully. Expecting people already in need of support to manage to bypass this deliberate inconvenience is simply unrealistic.
The company I work for used to maintain a solution based on this approach. It worked well until browser-vendors started tightening up security.
After that we had to come up with a different solution all together, because almost no users managed to configure our integration successfully.
(And that rewrite was a lot of work, so I can see why Cisco/WebEx has been postponing it as much as possible)
They could even, god forbid, accept that it's not possible instead of coming up with "clever" ways to make it possible.