how to properly do an automatic uninstall?

I first understood it is not possible. But it seems to be implemented in 
Firefox, so it must be.

Please help me, it is embarrashing to explain users to delete the files 
etc. by hand.

I have tried to do it with Install.uninstall. But how do I refer to 
Install when I'm not in install.js anymore? And some sources also say 
this does not work.

Also I tried jslib uninstallPackage:

var
     regkey = "Annotea/Ubimarks",
     uobj = new Uninstall(regkey);
   uobj.uninstallPackage();

But this does not work as it needs to refer to the uninstall xul wizard.
And if I open the wizard with

window.openDialog("chrome://jslib/content/install/uninstall.xul",
                       "jslibuninstall",
                       "chrome,width=800","Annotea/Ubimarks", function 
dotest() {dump("test\n");} );

There are no complaints, but it never opens the wizard window.

Marja