diff --git a/content.js b/content.js
index 4816eb2..09f0e45 100644
--- a/content.js
+++ b/content.js
@@ -837,9 +837,9 @@ class YTMBlockController {
             for (let j = 0; j < mutation.addedNodes.length; j++) {
               const node = mutation.addedNodes[j];
               if (node && node.nodeType === 1) { // Node.ELEMENT_NODE
-                const tagName = node.tagName ? node.tagName.toLowerCase() : '';
-                if (tagName === 'ytmusic-menu-popup-renderer' ||
-                    tagName === 'tp-yt-paper-listbox' ||
+                const tagName = node.tagName || '';
+                if (tagName === 'YTMUSIC-MENU-POPUP-RENDERER' ||
+                    tagName === 'TP-YT-PAPER-LISTBOX' ||
                     (node.querySelector && node.querySelector('ytmusic-menu-popup-renderer, tp-yt-paper-listbox'))) {
                   hasPopupChange = true;
                   break;
diff --git a/tests/menuObserver.test.js b/tests/menuObserver.test.js
new file mode 100644
index 0000000..69da6e6
--- /dev/null
+++ b/tests/menuObserver.test.js
@@ -0,0 +1,88 @@
+const test = require('node:test');
+const assert = require('node:assert');
+const { performance } = require('node:perf_hooks');
+
+test('MutationObserver tag matching performance benchmark', async (t) => {
+  await t.test('compares toLowerCase vs direct uppercase comparison', () => {
+    const mutations = [];
+    for (let i = 0; i < 500; i++) {
+      const addedNodes = [];
+      for (let j = 0; j < 20; j++) {
+        addedNodes.push({
+          nodeType: 1,
+          tagName: (i + j) % 7 === 0 ? 'YTMUSIC-MENU-POPUP-RENDERER' : 'DIV'
+        });
+      }
+      mutations.push({ addedNodes });
+    }
+
+    function checkBaseline(mutations) {
+      let hasPopupChange = false;
+      for (let i = 0; i < mutations.length; i++) {
+        const mutation = mutations[i];
+        if (mutation.addedNodes && mutation.addedNodes.length > 0) {
+          for (let j = 0; j < mutation.addedNodes.length; j++) {
+            const node = mutation.addedNodes[j];
+            if (node && node.nodeType === 1) {
+              const tagName = node.tagName ? node.tagName.toLowerCase() : '';
+              if (tagName === 'ytmusic-menu-popup-renderer' ||
+                  tagName === 'tp-yt-paper-listbox') {
+                hasPopupChange = true;
+                break;
+              }
+            }
+          }
+        }
+        if (hasPopupChange) break;
+      }
+      return hasPopupChange;
+    }
+
+    function checkOptimized(mutations) {
+      let hasPopupChange = false;
+      for (let i = 0; i < mutations.length; i++) {
+        const mutation = mutations[i];
+        if (mutation.addedNodes && mutation.addedNodes.length > 0) {
+          for (let j = 0; j < mutation.addedNodes.length; j++) {
+            const node = mutation.addedNodes[j];
+            if (node && node.nodeType === 1) {
+              const tagName = node.tagName || '';
+              if (tagName === 'YTMUSIC-MENU-POPUP-RENDERER' ||
+                  tagName === 'TP-YT-PAPER-LISTBOX') {
+                hasPopupChange = true;
+                break;
+              }
+            }
+          }
+        }
+        if (hasPopupChange) break;
+      }
+      return hasPopupChange;
+    }
+
+    // Warmup
+    for (let i = 0; i < 50; i++) {
+      checkBaseline(mutations);
+      checkOptimized(mutations);
+    }
+
+    const startBaseline = performance.now();
+    for (let i = 0; i < 2000; i++) {
+      checkBaseline(mutations);
+    }
+    const durationBaseline = performance.now() - startBaseline;
+
+    const startOptimized = performance.now();
+    for (let i = 0; i < 2000; i++) {
+      checkOptimized(mutations);
+    }
+    const durationOptimized = performance.now() - startOptimized;
+
+    const speedup = ((durationBaseline - durationOptimized) / durationBaseline) * 100;
+    console.log(`[MutationObserver Benchmark] Baseline (toLowerCase): ${durationBaseline.toFixed(2)}ms`);
+    console.log(`[MutationObserver Benchmark] Optimized (uppercase):   ${durationOptimized.toFixed(2)}ms`);
+    console.log(`[MutationObserver Benchmark] Speedup: ${speedup.toFixed(2)}%`);
+
+    assert.strictEqual(checkBaseline(mutations), checkOptimized(mutations));
+  });
+});