I too have the exact same issue. I am using OSX Lion 10.7.4 one one computer AND Mountail Lion OSX 10.8 on the other. Both versions of Safari ar 6.0 Neither of them work. I have installed Skype and Click to Call on a PC and my account works well so I am sure this is a Mac issue. Also I have spent probably 6 or 7 hrs with the Support chats CSR and they were not even aware the feature was supported for Mac.....until I showed the URL. Please contact me if you have further questions or coments so we can make this work.
I also have the same problem. Its been two months since last post, has skype or anyone figured it out. Im running OS X 10.5.8 Please post the solution if any, many people probably having same issue.