diff --git a/js/src/builtin/TestingFunctions.cpp b/js/src/builtin/TestingFunctions.cpp
index 1e61ca33dc1f..6e7218dd20be 100644
--- a/js/src/builtin/TestingFunctions.cpp
+++ b/js/src/builtin/TestingFunctions.cpp
@@ -1377,12 +1377,11 @@ ShellObjectMetadataCallback(JSContext* cx, JSObject*)
 }
 
 static bool
-SetObjectMetadataCallback(JSContext* cx, unsigned argc, Value* vp)
+EnableShellObjectMetadataCallback(JSContext* cx, unsigned argc, Value* vp)
 {
     CallArgs args = CallArgsFromVp(argc, vp);
 
-    bool enabled = args.length() ? ToBoolean(args[0]) : false;
-    SetObjectMetadataCallback(cx, enabled ? ShellObjectMetadataCallback : nullptr);
+    SetObjectMetadataCallback(cx, ShellObjectMetadataCallback);
 
     args.rval().setUndefined();
     return true;
@@ -2934,9 +2933,9 @@ gc::ZealModeHelpText),
 "isRelazifiableFunction(fun)",
 "  Ture if fun is a JSFunction with a relazifiable JSScript."),
 
-    JS_FN_HELP("setObjectMetadataCallback", SetObjectMetadataCallback, 1, 0,
-"setObjectMetadataCallback(fn)",
-"  Specify function to supply metadata for all newly created objects."),
+    JS_FN_HELP("enableShellObjectMetadataCallback", EnableShellObjectMetadataCallback, 0, 0,
+"enableShellObjectMetadataCallback()",
+"  Use ShellObjectMetadataCallback to supply metadata for all newly created objects."),
 
     JS_FN_HELP("getObjectMetadata", GetObjectMetadata, 1, 0,
 "getObjectMetadata(obj)",
diff --git a/js/src/jit-test/tests/baseline/metadata-hook-on-stack.js b/js/src/jit-test/tests/baseline/metadata-hook-on-stack.js
index 7064772f1afe..a4df753898b8 100644
--- a/js/src/jit-test/tests/baseline/metadata-hook-on-stack.js
+++ b/js/src/jit-test/tests/baseline/metadata-hook-on-stack.js
@@ -4,7 +4,7 @@
 function f() {
     for (var i=0; i<100; i++) {
 	if (i === 20)
-	    setObjectMetadataCallback(true);
+	    enableShellObjectMetadataCallback();
 	var o = {x: 1};
 	if (i >= 20) {
 	    var md = getObjectMetadata(o);
diff --git a/js/src/jit-test/tests/basic/bug951213.js b/js/src/jit-test/tests/basic/bug951213.js
index 4f773cf03b77..be4f27261b6c 100644
--- a/js/src/jit-test/tests/basic/bug951213.js
+++ b/js/src/jit-test/tests/basic/bug951213.js
@@ -1,5 +1,5 @@
 
-setObjectMetadataCallback(function(obj) {});
+enableShellObjectMetadataCallback();
 function foo(x, y) {
   this.g = x + y;
 }
diff --git a/js/src/jit-test/tests/basic/bug951346.js b/js/src/jit-test/tests/basic/bug951346.js
index 2034d6ba0f8f..fa68da631642 100644
--- a/js/src/jit-test/tests/basic/bug951346.js
+++ b/js/src/jit-test/tests/basic/bug951346.js
@@ -1,3 +1,3 @@
 
-setObjectMetadataCallback(function(obj) {});
+enableShellObjectMetadataCallback();
 eval(uneval({'-1':true}));
diff --git a/js/src/jit-test/tests/basic/bug951632.js b/js/src/jit-test/tests/basic/bug951632.js
index a2e6a89adcdb..fa0dbd3bebec 100644
--- a/js/src/jit-test/tests/basic/bug951632.js
+++ b/js/src/jit-test/tests/basic/bug951632.js
@@ -1,4 +1,4 @@
-setObjectMetadataCallback(true);
+enableShellObjectMetadataCallback();
 var g = newGlobal()
 g.eval("function f(a) { return h(); }");
 g.h = function () {
diff --git a/js/src/jit-test/tests/basic/metadata-hook.js b/js/src/jit-test/tests/basic/metadata-hook.js
index 38b24a8d7e79..a589b381afe4 100644
--- a/js/src/jit-test/tests/basic/metadata-hook.js
+++ b/js/src/jit-test/tests/basic/metadata-hook.js
@@ -1,5 +1,5 @@
 
-setObjectMetadataCallback(true);
+enableShellObjectMetadataCallback();
 
 function Foo() {
   this.x = 0;
diff --git a/js/src/jit-test/tests/debug/Memory-trackingAllocationSites-03.js b/js/src/jit-test/tests/debug/Memory-trackingAllocationSites-03.js
index 08b904777150..0447d7d32234 100644
--- a/js/src/jit-test/tests/debug/Memory-trackingAllocationSites-03.js
+++ b/js/src/jit-test/tests/debug/Memory-trackingAllocationSites-03.js
@@ -4,8 +4,6 @@ load(libdir + "asserts.js");
 
 let dbg1, dbg2, root1, root2;
 
-function FakeMetadata() {}
-
 function isTrackingAllocations(global, dbgObj) {
   const site = dbgObj.makeDebuggeeValue(global.eval("({})")).allocationSite;
   if (site) {
@@ -65,7 +63,7 @@ test("Setting trackingAllocationSites to true should throw if the debugger " +
        let d1r2 = dbg1.addDebuggee(root2);
 
        // Can't install allocation hooks for root2 with this set.
-       root2.setObjectMetadataCallback(function () { return new FakeMetadata; });
+       root2.enableShellObjectMetadataCallback();
 
        assertThrowsInstanceOf(() => dbg1.memory.trackingAllocationSites = true,
                               Error);
@@ -96,7 +94,7 @@ test("Re-enabling throws an error if we can't reinstall allocations tracking " +
        let d1r2 = dbg1.addDebuggee(root2);
 
        // Can't install allocation hooks for root2 with this set.
-       root2.setObjectMetadataCallback(function () { return new FakeMetadata; });
+       root2.enableShellObjectMetadataCallback();
 
        assertThrowsInstanceOf(() => dbg1.enabled = true,
                               Error);
diff --git a/js/src/jit-test/tests/gc/bug-1148383.js b/js/src/jit-test/tests/gc/bug-1148383.js
index eea1d6c1ddcc..fcd7fcc0cb81 100644
--- a/js/src/jit-test/tests/gc/bug-1148383.js
+++ b/js/src/jit-test/tests/gc/bug-1148383.js
@@ -14,6 +14,6 @@ function reportCompare () {
 }
 reportCompare();
 gczeal(4, 1000);
-setObjectMetadataCallback(true);
+enableShellObjectMetadataCallback();
 for (var i = 0; i < 10000; ++i)
   reportCompare();
diff --git a/js/src/jit-test/tests/gc/bug-886560.js b/js/src/jit-test/tests/gc/bug-886560.js
index 9880e9194187..bdd6a80c9cb1 100644
--- a/js/src/jit-test/tests/gc/bug-886560.js
+++ b/js/src/jit-test/tests/gc/bug-886560.js
@@ -1,5 +1,9 @@
 // |jit-test| error: x is not defined
-setObjectMetadataCallback(function(obj) {
+
+// enableShellObjectMetadataCallback ignores its argument, because we don't
+// permit metadata callbacks to run JS any more, so this test may be
+// unnecessary. We'll preserve its structure just in case.
+enableShellObjectMetadataCallback(function(obj) {
     var res = {};
     return res;
   });
diff --git a/js/src/jit-test/tests/gc/bug-935022.js b/js/src/jit-test/tests/gc/bug-935022.js
index b4a5eb0fe614..d47bc3c9b555 100644
--- a/js/src/jit-test/tests/gc/bug-935022.js
+++ b/js/src/jit-test/tests/gc/bug-935022.js
@@ -1,4 +1,4 @@
 function callback(obj) {}
-setObjectMetadataCallback(callback);
+enableShellObjectMetadataCallback();
 gczeal(7);
 var statusitems = [];
diff --git a/js/src/jit-test/tests/gc/bug-945280.js b/js/src/jit-test/tests/gc/bug-945280.js
index 48b9695d8ed4..9340c6d3fb84 100644
--- a/js/src/jit-test/tests/gc/bug-945280.js
+++ b/js/src/jit-test/tests/gc/bug-945280.js
@@ -1,4 +1,4 @@
 gczeal(7,1);
-setObjectMetadataCallback(setObjectMetadataCallback);
+enableShellObjectMetadataCallback();
 gczeal(false);
 var statusitems = [];
diff --git a/js/src/jit-test/tests/gc/bug-945285.js b/js/src/jit-test/tests/gc/bug-945285.js
index c2d83d215f82..d2d6afd0c8c2 100644
--- a/js/src/jit-test/tests/gc/bug-945285.js
+++ b/js/src/jit-test/tests/gc/bug-945285.js
@@ -1,3 +1,3 @@
 gczeal(11);
 function callback(obj) {}
-setObjectMetadataCallback(callback);
+enableShellObjectMetadataCallback();
diff --git a/js/src/jit-test/tests/gc/bug-961741.js b/js/src/jit-test/tests/gc/bug-961741.js
index a4d0ee7a9d8b..c1777fb84de8 100644
--- a/js/src/jit-test/tests/gc/bug-961741.js
+++ b/js/src/jit-test/tests/gc/bug-961741.js
@@ -1,5 +1,5 @@
 function r() {
     for (var x in undefined) {}
 }
-setObjectMetadataCallback(true);
+enableShellObjectMetadataCallback();
 r();
diff --git a/js/src/jit-test/tests/ion/bug1006899.js b/js/src/jit-test/tests/ion/bug1006899.js
index 6502bd7daf2d..f9549d6436ac 100644
--- a/js/src/jit-test/tests/ion/bug1006899.js
+++ b/js/src/jit-test/tests/ion/bug1006899.js
@@ -7,7 +7,7 @@ this.__defineGetter__("x",
   }
 );
 function callback(obj) {}
-setObjectMetadataCallback(callback);
+enableShellObjectMetadataCallback();
 evaluate("\
 var { ArrayType, StructType, uint32 } = TypedObject;\
   var L = 1024;\
diff --git a/js/src/jit-test/tests/ion/bug1054241.js b/js/src/jit-test/tests/ion/bug1054241.js
index 80caf8d7a279..fb45badaf70d 100644
--- a/js/src/jit-test/tests/ion/bug1054241.js
+++ b/js/src/jit-test/tests/ion/bug1054241.js
@@ -1,7 +1,7 @@
 setJitCompilerOption("baseline.warmup.trigger", 10);
 setJitCompilerOption("ion.warmup.trigger", 20);
 
-setObjectMetadataCallback(true);
+enableShellObjectMetadataCallback();
 (function(){
   for(var i = 0; i < 100; i++) {
     try{
diff --git a/js/src/jit-test/tests/ion/bug1057598.js b/js/src/jit-test/tests/ion/bug1057598.js
index 36c84c0cade4..be3b5173c769 100644
--- a/js/src/jit-test/tests/ion/bug1057598.js
+++ b/js/src/jit-test/tests/ion/bug1057598.js
@@ -1,4 +1,7 @@
-setObjectMetadataCallback(function( r, ... d)  {});
+// enableShellObjectMetadataCallback ignores its argument, because we don't
+// permit metadata callbacks to run JS any more, so this test may be
+// unnecessary. We'll preserve its structure just in case.
+enableShellObjectMetadataCallback(function( r, ... d)  {});
 setJitCompilerOption("ion.warmup.trigger", 20);
 var uceFault = function (i) {
     if (i > 98)
diff --git a/js/src/jit-test/tests/ion/recover-lambdas-bug1113940.js b/js/src/jit-test/tests/ion/recover-lambdas-bug1113940.js
index 0d0ebf894d40..dd18e82a69f1 100644
--- a/js/src/jit-test/tests/ion/recover-lambdas-bug1113940.js
+++ b/js/src/jit-test/tests/ion/recover-lambdas-bug1113940.js
@@ -4,7 +4,11 @@ gczeal(14);
 // The object metadata callback can iterate over the stack. Thus during the
 // allocation of the lambda we might inspect the stack which is still incomplete
 // because the lambda is not yet reconstructed.
-setObjectMetadataCallback(function() {});
+//
+// enableShellObjectMetadataCallback ignores its argument, because we don't
+// permit metadata callbacks to run JS any more, so this test may be
+// unnecessary. We'll preserve its structure just in case.
+enableShellObjectMetadataCallback(function() {});
 function f() {
     (function() {
         '' ^ Object
@@ -17,7 +21,8 @@ for (var j = 0; j < 99; ++j) {
 
 try {
   x = true;
-  setObjectMetadataCallback(function([x, y, z], ... Debugger) {});
+  // Same comment as above.
+  enableShellObjectMetadataCallback(function([x, y, z], ... Debugger) {});
   for (var i = 0; i < 10; ++i) {
     var f = function() {
       function g() {