I parsed document.URL in opened page for specific parameter and it worked for me. E.g.
function __onLoad()
{
var p = $.url(document.URL);
alert(p.param("url"));
}
And two possible reasons for missed message:
- You did not add message event listener on your page
- You called dispatchMessage before event listener was added
Check Safari development doc at https://developer.apple.com/library/archive/documentation/Tools/Conceptual/SafariExtensionGuide/MessagesandProxies/MessagesandProxies.html