diff --git a/js/xpconnect/src/XPCWrappedJSClass.cpp b/js/xpconnect/src/XPCWrappedJSClass.cpp
index e82bac0b7f9a..939294c1dc38 100644
--- a/js/xpconnect/src/XPCWrappedJSClass.cpp
+++ b/js/xpconnect/src/XPCWrappedJSClass.cpp
@@ -10,12 +10,10 @@
 #include "jsprf.h"
 #include "nsArrayEnumerator.h"
 #include "nsContentUtils.h"
-#include "nsINamed.h"
 #include "nsIScriptError.h"
 #include "nsWrapperCache.h"
 #include "AccessCheck.h"
 #include "nsJSUtils.h"
-#include "nsPrintfCString.h"
 #include "mozilla/Attributes.h"
 #include "mozilla/dom/BindingUtils.h"
 #include "mozilla/dom/DOMException.h"
@@ -451,97 +449,6 @@ NS_DEFINE_STATIC_IID_ACCESSOR(WrappedJSIdentity,
 
 /***************************************************************************/
 
-namespace {
-
-class WrappedJSNamed final : public nsINamed
-{
-    nsCString mName;
-
-    ~WrappedJSNamed() {}
-
-public:
-    NS_DECL_ISUPPORTS
-
-    WrappedJSNamed(const nsACString& aName) : mName(aName) {}
-
-    NS_IMETHOD GetName(nsACString& aName) override
-    {
-        aName = mName;
-        aName.AppendLiteral(":JS");
-        return NS_OK;
-    }
-};
-
-NS_IMPL_ISUPPORTS(WrappedJSNamed, nsINamed)
-
-nsCString
-GetFunctionName(JSContext* cx, HandleObject obj)
-{
-    RootedObject inner(cx, js::UncheckedUnwrap(obj));
-    JSAutoCompartment ac(cx, inner);
-
-    RootedFunction fun(cx, JS_GetObjectFunction(inner));
-    if (!fun) {
-        // If the object isn't a function, it's likely that it has a single
-        // function property (for things like nsITimerCallback). In this case,
-        // return the name of that function property.
-
-        Rooted<IdVector> idArray(cx, IdVector(cx));
-        if (!JS_Enumerate(cx, inner, &idArray)) {
-            JS_ClearPendingException(cx);
-            return nsCString("error");
-        }
-
-        if (idArray.length() != 1)
-            return nsCString("nonfunction");
-
-        RootedId id(cx, idArray[0]);
-        RootedValue v(cx);
-        if (!JS_GetPropertyById(cx, inner, id, &v)) {
-            JS_ClearPendingException(cx);
-            return nsCString("nonfunction");
-        }
-
-        if (!v.isObject())
-            return nsCString("nonfunction");
-
-        RootedObject vobj(cx, &v.toObject());
-        return GetFunctionName(cx, vobj);
-    }
-
-    RootedString funName(cx, JS_GetFunctionDisplayId(fun));
-    RootedScript script(cx, JS_GetFunctionScript(cx, fun));
-    const char* filename = script ? JS_GetScriptFilename(script) : "anonymous";
-    const char* filenameSuffix = strrchr(filename, '/');
-
-    if (filenameSuffix) {
-        filenameSuffix++;
-    } else {
-        filenameSuffix = filename;
-    }
-
-    nsCString displayName("anonymous");
-    if (funName) {
-        nsCString* displayNamePtr = &displayName;
-        RootedValue funNameVal(cx, StringValue(funName));
-        if (!XPCConvert::JSData2Native(&displayNamePtr, funNameVal, nsXPTType::T_UTF8STRING,
-                                       nullptr, nullptr))
-        {
-            JS_ClearPendingException(cx);
-            return nsCString("anonymous");
-        }
-    }
-
-    displayName.Append('[');
-    displayName.Append(filenameSuffix, strlen(filenameSuffix));
-    displayName.Append(']');
-    return displayName;
-}
-
-} // anonymous namespace
-
-/***************************************************************************/
-
 // static
 bool
 nsXPCWrappedJSClass::IsWrappedJS(nsISupports* aPtr)
@@ -683,16 +590,6 @@ nsXPCWrappedJSClass::DelegatedQueryInterface(nsXPCWrappedJS* self,
         }
     }
 
-    // If we're asked to QI to nsINamed, we pretend that this is possible. We'll
-    // try to return a name that makes sense for the wrapped JS value.
-    if (aIID.Equals(NS_GET_IID(nsINamed))) {
-        RootedObject obj(RootingCx(), self->GetJSObject());
-        nsCString name = GetFunctionName(ccx, obj);
-        RefPtr<WrappedJSNamed> named = new WrappedJSNamed(name);
-        *aInstancePtr = named.forget().take();
-        return NS_OK;
-    }
-
     // else...
     // no can do
     *aInstancePtr = nullptr;
diff --git a/js/xpconnect/tests/unit/test_function_names.js b/js/xpconnect/tests/unit/test_function_names.js
deleted file mode 100644
index 9b325976675b..000000000000
--- a/js/xpconnect/tests/unit/test_function_names.js
+++ /dev/null
@@ -1,41 +0,0 @@
-/* Any copyright is dedicated to the Public Domain.
- * http://creativecommons.org/publicdomain/zero/1.0/ */
-
-var Cu = Components.utils;
-var Cc = Components.classes;
-var Ci = Components.interfaces;
-
-function callback() {}
-
-let sandbox = Cu.Sandbox(this);
-let callbackWrapped = Cu.evalInSandbox("(function wrapped() {})", sandbox);
-
-function run_test() {
-  let functions = [
-    [{ notify: callback }, "callback[test_function_names.js]:JS"],
-    [{ notify: { notify: callback } }, "callback[test_function_names.js]:JS"],
-    [callback, "callback[test_function_names.js]:JS"],
-    [function() {}, "run_test/functions<[test_function_names.js]:JS"],
-    [function foobar() {}, "foobar[test_function_names.js]:JS"],
-    [function Δ() {}, "Δ[test_function_names.js]:JS"],
-    [{ notify1: callback, notify2: callback }, "nonfunction:JS"],
-    [{ notify: 10 }, "nonfunction:JS"],
-    [{}, "nonfunction:JS"],
-    [{ notify: callbackWrapped }, "wrapped[test_function_names.js]:JS"],
-  ];
-
-  // Use the observer service so we can get double-wrapped functions.
-  var obs = Cc["@mozilla.org/observer-service;1"].getService(Ci.nsIObserverService);
-
-  function observer(subject, topic, data)
-  {
-    let named = subject.QueryInterface(Ci.nsINamed);
-    do_check_eq(named.name, data);
-    dump(`name: ${named.name}\n`);
-  }
-  obs.addObserver(observer, "test-obs-fun", false);
-
-  for (let [f, requiredName] of functions) {
-    obs.notifyObservers(f, "test-obs-fun", requiredName);
-  }
-}
diff --git a/js/xpconnect/tests/unit/xpcshell.ini b/js/xpconnect/tests/unit/xpcshell.ini
index 728522b72fb5..0d9a9faa96a5 100644
--- a/js/xpconnect/tests/unit/xpcshell.ini
+++ b/js/xpconnect/tests/unit/xpcshell.ini
@@ -136,4 +136,3 @@ head = head_watchdog.js
 [test_xray_regexp.js]
 [test_resolve_dead_promise.js]
 [test_asyncLoadSubScriptError.js]
-[test_function_names.js]
diff --git a/xpcom/threads/nsINamed.idl b/xpcom/threads/nsINamed.idl
index cdb7d88f30eb..46094a671106 100644
--- a/xpcom/threads/nsINamed.idl
+++ b/xpcom/threads/nsINamed.idl
@@ -20,5 +20,5 @@ interface nsINamed : nsISupports
      * WARNING: This attribute will be included in telemetry, so it should
      * never contain privacy sensitive information.
      */
-    readonly attribute AUTF8String name;
+    readonly attribute ACString name;
 };