My point was that the web app will work in a web browser on older Macs, but the designated desktop application only works in Mavericks and higher. Unsupported Macs will now be able to use the web app, at the very least. Your comment regarding Chrome/Firefox has nothing to do with them discontinuing support for older Macs for their main application.
But going back to your Chrome/Firefox comment, Firefox will work, but only the Windows version of Chrome will work with the Skype web API. So Firefox or Safari 6 will work.