The Tor Browser / file revision

 // The script and environment of a non-debuggee function are null.

 var g = newGlobal();

 g.eval('function f() { return "from f"; }');

 var dbg = new Debugger;

 var gw = dbg.makeGlobalObjectReference(g);

 var fw = gw.getOwnPropertyDescriptor('f').value;

 // g is not a debuggee, so we can't fetch f's script or environment.

 assertEq(fw.script, null);

 assertEq(fw.environment, null);

 // If we add g as a debuggee, we can fetch f's script and environment.

 dbg.addDebuggee(g);

 var fscript = fw.script;

 var fenv = fw.environment;

 assertEq(fscript instanceof Debugger.Script, true);

 assertEq(fenv instanceof Debugger.Environment, true);

 // Removing g as a debuggee makes the script and environment inaccessible again.

 dbg.removeDebuggee(g);

 assertEq(fw.script, null);

 assertEq(fw.environment, null);