diff --git a/_sass/styles.scss b/_sass/styles.scss
index da2d39e1..c095a4a2 100644
--- a/_sass/styles.scss
+++ b/_sass/styles.scss
@@ -739,6 +739,21 @@ table tr:nth-child(2n) {
   padding: 0.8rem;
 }
 
+.gamepad-browser-warning {
+  margin-inline: auto;
+  max-width: 46rem;
+}
+
+.gamepad-browser-warning[hidden] {
+  display: none;
+}
+
+.gamepad-browser-warning a {
+  font-weight: 600;
+  overflow-wrap: anywhere;
+  text-decoration: underline;
+}
+
 .gamepad-device-details > summary {
   align-items: center;
   cursor: pointer;
@@ -847,6 +862,12 @@ table tr:nth-child(2n) {
     padding: 0.65rem 0.85rem;
   }
 
+  .gamepad-tester.has-gamepad .gamepad-browser-warning {
+    margin-top: 0.75rem !important;
+    max-width: none;
+    padding: 0.55rem 0.75rem;
+  }
+
   .gamepad-tester.has-gamepad .gamepad-selector-panel {
     display: grid;
     grid-template-columns: 13rem minmax(0, 1fr);
diff --git a/assets/js/gamepad-tester.js b/assets/js/gamepad-tester.js
index bf9a9583..8d2bacf3 100644
--- a/assets/js/gamepad-tester.js
+++ b/assets/js/gamepad-tester.js
@@ -5,6 +5,13 @@ function createDPadButtonVisuals(shapes) {
     }));
 }
 
+const FIREFOX_SWITCH_GAMEPAD_FIXED_VERSION = 155;
+
+function getFirefoxMajorVersion(userAgent) {
+    const match = /\bFirefox\/(\d+)/.exec(userAgent);
+    return match ? Number.parseInt(match[1], 10) : null;
+}
+
 document.addEventListener('DOMContentLoaded', function() {
     const gamepadHelper = new GamepadHelper()
     const gamepadHelperVersion = globalThis.gamepadHelperVersion;
@@ -17,6 +24,8 @@ document.addEventListener('DOMContentLoaded', function() {
     const gamepadTester = document.getElementById('GamepadTester');
     const gamepadStatus = document.getElementById('gamepad-status');
     const gamepadStatusMessage = document.getElementById('gamepad-status-message');
+    const firefoxSwitchWarning = document.getElementById('firefox-switch-warning');
+    const firefoxMajorVersion = getFirefoxMajorVersion(navigator.userAgent);
     let gamepadVisualButtons = new Map();
     let gamepadVisualSticks = [];
     let gamepadVisualTriggers = new Map();
@@ -205,7 +214,15 @@ document.addEventListener('DOMContentLoaded', function() {
 
         const gamepadIndices = Object.keys(gamepads);
         const hasGamepads = gamepadIndices.length > 0;
+        const hasNintendoSwitchController = Object.values(gamepads).some(gamepad =>
+            gamepadHelper.detectControllerType(gamepad.id) === gamepadHelper.CONTROLLER_TYPES.SWITCH
+        );
         gamepadTester.classList.toggle('has-gamepad', hasGamepads);
+        firefoxSwitchWarning.hidden = !(
+            firefoxMajorVersion !== null
+            && firefoxMajorVersion < FIREFOX_SWITCH_GAMEPAD_FIXED_VERSION
+            && hasNintendoSwitchController
+        );
 
         if (hasGamepads) {
             gamepadSelectorContainer.style.removeProperty('display');
diff --git a/gamepad-tester.html b/gamepad-tester.html
index 0e52e378..2d56e0cc 100644
--- a/gamepad-tester.html
+++ b/gamepad-tester.html
@@ -36,6 +36,15 @@ <h2 class="display-6 fw-bolder mb-2">Gamepad Tester</h2>
             </p>
         </header>
 
+        <div id="firefox-switch-warning" class="gamepad-browser-warning gamepad-inline-notice mt-3" aria-live="polite" hidden>
+            <i class="fas fa-triangle-exclamation mt-1" aria-hidden="true"></i>
+            <span>
+                Firefox versions before 155 can report incorrect buttons and axes for Nintendo Switch controllers.
+                Update to Firefox 155 or later, or use another current browser.
+                Details: <a href="https://bugzilla.mozilla.org/show_bug.cgi?id=1704419" target="_blank" rel="noopener noreferrer">https://bugzilla.mozilla.org/show_bug.cgi?id=1704419</a>
+            </span>
+        </div>
+
         <section class="gamepad-selector-panel mt-4" id="gamepad-selector-container" style="display: none;" aria-labelledby="gamepad-selector-heading">
             <div class="gamepad-selector-heading">
                 <div>