diff --git a/js/src/shell/js.cpp b/js/src/shell/js.cpp
index 870e6b58be76..01e43a320448 100644
--- a/js/src/shell/js.cpp
+++ b/js/src/shell/js.cpp
@@ -12956,9 +12956,6 @@ bool SetGlobalOptionsPreJSInit(const OptionParser& op) {
   if (op.getBoolOption("enable-atomics-pause")) {
     JS::Prefs::setAtStartup_experimental_atomics_pause(true);
   }
-  if (op.getBoolOption("enable-error-iserror")) {
-    JS::Prefs::set_experimental_error_iserror(true);
-  }
 #ifdef NIGHTLY_BUILD
   if (op.getBoolOption("enable-async-iterator-helpers")) {
     JS::Prefs::setAtStartup_experimental_async_iterator_helpers(true);
@@ -12966,6 +12963,9 @@ bool SetGlobalOptionsPreJSInit(const OptionParser& op) {
   if (op.getBoolOption("enable-symbols-as-weakmap-keys")) {
     JS::Prefs::setAtStartup_experimental_symbols_as_weakmap_keys(true);
   }
+  if (op.getBoolOption("enable-error-iserror")) {
+    JS::Prefs::set_experimental_error_iserror(true);
+  }
   if (op.getBoolOption("enable-iterator-sequencing")) {
     JS::Prefs::setAtStartup_experimental_iterator_sequencing(true);
   }
diff --git a/js/src/vm/ErrorObject.cpp b/js/src/vm/ErrorObject.cpp
index acf0a1a65b52..99d4567d84a8 100644
--- a/js/src/vm/ErrorObject.cpp
+++ b/js/src/vm/ErrorObject.cpp
@@ -979,6 +979,8 @@ static bool exn_toSource(JSContext* cx, unsigned argc, Value* vp) {
   return true;
 }
 
+#ifdef NIGHTLY_BUILD
+
 /**
  * Error.isError Proposal
  * Error.isError ( arg )
@@ -1026,6 +1028,7 @@ static bool exn_isError(JSContext* cx, unsigned argc, Value* vp) {
   args.rval().setBoolean(false);
   return true;
 }
+#endif
 
 // The below is the "documentation" from https://v8.dev/docs/stack-trace-api
 //
diff --git a/js/src/vm/JSObject.cpp b/js/src/vm/JSObject.cpp
index 303fff57c79e..204280889e71 100644
--- a/js/src/vm/JSObject.cpp
+++ b/js/src/vm/JSObject.cpp
@@ -2259,10 +2259,6 @@ JS_PUBLIC_API bool js::ShouldIgnorePropertyDefinition(JSContext* cx,
         id == NameToId(cx->names().try_)) {
       return true;
     }
-    if (!JS::Prefs::experimental_error_iserror() &&
-        id == NameToId(cx->names().isError)) {
-      return true;
-    }
   }
 
 #ifdef JS_HAS_TEMPORAL_API
@@ -2277,6 +2273,10 @@ JS_PUBLIC_API bool js::ShouldIgnorePropertyDefinition(JSContext* cx,
   // to realize is that this is a -constructor function-, not a function
   // on the prototype; and the proto of the constructor is JSProto_Function.
   if (key == JSProto_Function) {
+    if (!JS::Prefs::experimental_error_iserror() &&
+        id == NameToId(cx->names().isError)) {
+      return true;
+    }
     if (!JS::Prefs::experimental_iterator_range() &&
         (id == NameToId(cx->names().range))) {
       return true;
diff --git a/modules/libpref/init/StaticPrefList.yaml b/modules/libpref/init/StaticPrefList.yaml
index 79a43f2b70cd..c2f60df01274 100644
--- a/modules/libpref/init/StaticPrefList.yaml
+++ b/modules/libpref/init/StaticPrefList.yaml
@@ -8512,18 +8512,11 @@
   set_spidermonkey_pref: startup
 
   # Experimental support for Atomics.pause in JavaScript.
-- name: javascript.options.experimental.atomics_pause
-  type: bool
-  value: true
-  mirror: always
-  set_spidermonkey_pref: startup
-
-  # Experimental support for Error.isError in JavaScript.
-- name: javascript.options.experimental.error_iserror
-  type: bool
-  value: true
-  mirror: always
-  set_spidermonkey_pref: always
+-   name: javascript.options.experimental.atomics_pause
+    type: bool
+    value: true
+    mirror: always
+    set_spidermonkey_pref: startup
 
 #ifdef NIGHTLY_BUILD
   # Experimental support for Async Iterator Helpers in JavaScript.
@@ -8540,6 +8533,13 @@
     mirror: always
     set_spidermonkey_pref: startup
 
+  # Experimental support for Error.isError in JavaScript.
+-   name: javascript.options.experimental.error_iserror
+    type: bool
+    value: false
+    mirror: always
+    set_spidermonkey_pref: always
+
   # Experimental support for Iterator.range in JavaScript.
 -   name: javascript.options.experimental.iterator_range
     type: bool