Workaround.
There's an 'onContextMenu' event that is supported for Internet Explorer for Windows but not supported on IE for Mac. It's not part of the W3C spec but the latest versions of Mozilla support it as well. Problem on the Mac (I got to play on a brand new iMac today) is that when you hit Ctrl-Click, the OS intercepts it and never sends an event to the browser JavaScript.
To work around the problem, I just associated the popup menu with an Alt-Click. Have to train the users, but it should do the trick.