diff --git a/dom/script/ModuleLoader.cpp b/dom/script/ModuleLoader.cpp
index fb02a5900c3f..13054c4658b7 100644
--- a/dom/script/ModuleLoader.cpp
+++ b/dom/script/ModuleLoader.cpp
@@ -187,11 +187,10 @@ nsresult ModuleLoader::CompileOrFinishModuleScript(
     nsresult rv = aRequest->GetScriptSource(aCx, &maybeSource);
     NS_ENSURE_SUCCESS(rv, rv);
 
-    stencil = maybeSource.constructed<SourceText<char16_t>>()
-                  ? JS::CompileModuleScriptToStencil(
-                        aCx, aOptions, maybeSource.ref<SourceText<char16_t>>())
-                  : JS::CompileModuleScriptToStencil(
-                        aCx, aOptions, maybeSource.ref<SourceText<Utf8Unit>>());
+    auto compile = [&](auto& source) {
+      return JS::CompileModuleScriptToStencil(aCx, aOptions, source);
+    };
+    stencil = maybeSource.mapNonEmpty(compile);
   } else {
     MOZ_ASSERT(aRequest->IsBytecode());
     JS::DecodeOptions decodeOptions(aOptions);
diff --git a/dom/script/ScriptLoader.cpp b/dom/script/ScriptLoader.cpp
index a1cc5ead1c17..97e8d8b5effa 100644
--- a/dom/script/ScriptLoader.cpp
+++ b/dom/script/ScriptLoader.cpp
@@ -1589,17 +1589,18 @@ nsresult ScriptLoader::AttemptAsyncScriptCompile(ScriptLoadRequest* aRequest,
     nsresult rv = aRequest->GetScriptSource(cx, &maybeSource);
     NS_ENSURE_SUCCESS(rv, rv);
 
-    aRequest->GetScriptLoadContext()->mOffThreadToken =
-        maybeSource.constructed<SourceText<char16_t>>()
-            ? JS::CompileModuleToStencilOffThread(
-                  cx, options, maybeSource.ref<SourceText<char16_t>>(),
-                  OffThreadScriptLoaderCallback, static_cast<void*>(runnable))
-            : JS::CompileModuleToStencilOffThread(
-                  cx, options, maybeSource.ref<SourceText<Utf8Unit>>(),
-                  OffThreadScriptLoaderCallback, static_cast<void*>(runnable));
-    if (!aRequest->GetScriptLoadContext()->mOffThreadToken) {
+    auto compile = [&](auto& source) {
+      return JS::CompileModuleToStencilOffThread(
+          cx, options, source, OffThreadScriptLoaderCallback, runnable.get());
+    };
+
+    MOZ_ASSERT(!maybeSource.empty());
+    JS::OffThreadToken* token = maybeSource.mapNonEmpty(compile);
+    if (!token) {
       return NS_ERROR_OUT_OF_MEMORY;
     }
+
+    aRequest->GetScriptLoadContext()->mOffThreadToken = token;
   } else {
     MOZ_ASSERT(aRequest->IsTextSource());
 
@@ -1638,17 +1639,18 @@ nsresult ScriptLoader::AttemptAsyncScriptCompile(ScriptLoadRequest* aRequest,
       }
     }
 
-    aRequest->GetScriptLoadContext()->mOffThreadToken =
-        maybeSource.constructed<SourceText<char16_t>>()
-            ? JS::CompileToStencilOffThread(
-                  cx, options, maybeSource.ref<SourceText<char16_t>>(),
-                  OffThreadScriptLoaderCallback, static_cast<void*>(runnable))
-            : JS::CompileToStencilOffThread(
-                  cx, options, maybeSource.ref<SourceText<Utf8Unit>>(),
-                  OffThreadScriptLoaderCallback, static_cast<void*>(runnable));
-    if (!aRequest->GetScriptLoadContext()->mOffThreadToken) {
+    auto compile = [&](auto& source) {
+      return JS::CompileToStencilOffThread(
+          cx, options, source, OffThreadScriptLoaderCallback, runnable.get());
+    };
+
+    MOZ_ASSERT(!maybeSource.empty());
+    JS::OffThreadToken* token = maybeSource.mapNonEmpty(compile);
+    if (!token) {
       return NS_ERROR_OUT_OF_MEMORY;
     }
+
+    aRequest->GetScriptLoadContext()->mOffThreadToken = token;
   }
   signalOOM.release();
 
@@ -2170,10 +2172,11 @@ nsresult ScriptLoader::CompileOrDecodeClassicScript(
                                 MarkerInnerWindowIdFromJSContext(aCx),
                                 profilerLabelString);
 
+      auto compile = [&](auto& source) { return aExec.Compile(source); };
+
+      MOZ_ASSERT(!maybeSource.empty());
       TimeStamp startTime = TimeStamp::Now();
-      rv = maybeSource.constructed<SourceText<char16_t>>()
-               ? aExec.Compile(maybeSource.ref<SourceText<char16_t>>())
-               : aExec.Compile(maybeSource.ref<SourceText<Utf8Unit>>());
+      rv = maybeSource.mapNonEmpty(compile);
       mMainThreadParseTime += TimeStamp::Now() - startTime;
     }
   }
diff --git a/js/src/builtin/String.cpp b/js/src/builtin/String.cpp
index 30728d7bf85d..d25a9104fbb4 100644
--- a/js/src/builtin/String.cpp
+++ b/js/src/builtin/String.cpp
@@ -1281,11 +1281,11 @@ static JSString* ToUpperCase(JSContext* cx, JSLinearString* str) {
     }
   }
 
-  return newChars.constructed<Latin1Buffer>()
-             ? newChars.ref<Latin1Buffer>().toStringDontDeflate(cx,
-                                                                resultLength)
-             : newChars.ref<TwoByteBuffer>().toStringDontDeflate(cx,
-                                                                 resultLength);
+  auto toString = [&](auto& chars) {
+    return chars.toStringDontDeflate(cx, resultLength);
+  };
+
+  return newChars.mapNonEmpty(toString);
 }
 
 JSString* js::StringToUpperCase(JSContext* cx, HandleString string) {
diff --git a/mfbt/MaybeOneOf.h b/mfbt/MaybeOneOf.h
index 65c137bb7d38..769f18d5ddbc 100644
--- a/mfbt/MaybeOneOf.h
+++ b/mfbt/MaybeOneOf.h
@@ -131,6 +131,23 @@ class MOZ_NON_PARAM MaybeOneOf {
     }
   }
 
+  template <typename Func>
+  constexpr auto mapNonEmpty(Func&& aFunc) const {
+    MOZ_ASSERT(!empty());
+    if (state == SomeT1) {
+      return std::forward<Func>(aFunc)(as<T1>());
+    }
+    return std::forward<Func>(aFunc)(as<T2>());
+  }
+  template <typename Func>
+  constexpr auto mapNonEmpty(Func&& aFunc) {
+    MOZ_ASSERT(!empty());
+    if (state == SomeT1) {
+      return std::forward<Func>(aFunc)(as<T1>());
+    }
+    return std::forward<Func>(aFunc)(as<T2>());
+  }
+
  private:
   MaybeOneOf(const MaybeOneOf& aOther) = delete;
   const MaybeOneOf& operator=(const MaybeOneOf& aOther) = delete;