diff --git a/.changeset/tidy-toolbar-subscriptions.md b/.changeset/tidy-toolbar-subscriptions.md
new file mode 100644
index 000000000..5c8b68fe6
--- /dev/null
+++ b/.changeset/tidy-toolbar-subscriptions.md
@@ -0,0 +1,5 @@
+---
+"@reflag/browser-sdk": patch
+---
+
+Unsubscribe toolbar flag listeners when the toolbar is unmounted or switches clients.
diff --git a/packages/browser-sdk/src/toolbar/Toolbar.tsx b/packages/browser-sdk/src/toolbar/Toolbar.tsx
index 363074469..8c8ac5200 100644
--- a/packages/browser-sdk/src/toolbar/Toolbar.tsx
+++ b/packages/browser-sdk/src/toolbar/Toolbar.tsx
@@ -68,7 +68,7 @@ export default function Toolbar({
 
   useEffect(() => {
     updateFlags();
-    reflagClient.on("flagsUpdated", updateFlags);
+    return reflagClient.on("flagsUpdated", updateFlags);
   }, [reflagClient, updateFlags]);
 
   const [search, setSearch] = useState<string | null>(null);
diff --git a/packages/browser-sdk/test/cleanupUi.test.ts b/packages/browser-sdk/test/cleanupUi.test.ts
new file mode 100644
index 000000000..d3e5dd326
--- /dev/null
+++ b/packages/browser-sdk/test/cleanupUi.test.ts
@@ -0,0 +1,89 @@
+import { options } from "preact";
+import { afterEach, beforeEach, expect, test, vi } from "vitest";
+
+import { ReflagClient } from "../src/client";
+import { showToolbarToggle } from "../src/toolbar";
+import { toolbarContainerId } from "../src/ui/constants";
+import { cleanupUi } from "./cleanupUi";
+
+let effects: (() => void)[];
+let renders: (() => void)[];
+const originalRaf = options.requestAnimationFrame;
+const originalDebounce = options.debounceRendering;
+
+beforeEach(() => {
+  effects = [];
+  renders = [];
+  // Hold the actual Preact callbacks so teardown timing is deterministic.
+  options.requestAnimationFrame = (callback) => effects.push(callback);
+  options.debounceRendering = (callback) => renders.push(callback);
+});
+
+function drainCallbacks() {
+  while (effects.length || renders.length) {
+    effects.shift()?.();
+    renders.shift()?.();
+  }
+}
+
+function withoutSessionStorage(callback: () => void) {
+  const descriptor = Object.getOwnPropertyDescriptor(
+    globalThis,
+    "sessionStorage",
+  )!;
+  Reflect.deleteProperty(globalThis, "sessionStorage");
+  try {
+    callback();
+  } finally {
+    Object.defineProperty(globalThis, "sessionStorage", descriptor);
+  }
+}
+
+function mountToolbar() {
+  const client = new ReflagClient({
+    publishableKey: "test-key",
+    offline: true,
+    toolbar: false,
+  });
+  const unsubscribe = vi.fn();
+  const on = vi.spyOn(client, "on").mockReturnValue(unsubscribe);
+  showToolbarToggle({ reflagClient: client });
+  expect(document.getElementById(toolbarContainerId)).not.toBeNull();
+  return { on, unsubscribe };
+}
+
+afterEach(() => {
+  cleanupUi();
+  drainCallbacks();
+  options.requestAnimationFrame = originalRaf;
+  options.debounceRendering = originalDebounce;
+  vi.restoreAllMocks();
+});
+
+test("unmounts before a delayed toolbar effect can run after jsdom teardown", () => {
+  const { on } = mountToolbar();
+  expect(effects.length).toBeGreaterThan(0);
+
+  cleanupUi();
+
+  withoutSessionStorage(() => {
+    expect(drainCallbacks).not.toThrow();
+  });
+  expect(on).not.toHaveBeenCalled();
+  expect(document.getElementById(toolbarContainerId)).toBeNull();
+});
+
+test("cancels queued toolbar renders and unsubscribes mounted effects", () => {
+  const { unsubscribe } = mountToolbar();
+  // Run useEffect: updateFlags queues a render and subscribes to flagsUpdated.
+  while (effects.length) effects.shift()!();
+  expect(renders.length).toBeGreaterThan(0);
+
+  cleanupUi();
+
+  withoutSessionStorage(() => {
+    expect(drainCallbacks).not.toThrow();
+  });
+  expect(unsubscribe).toHaveBeenCalledOnce();
+  expect(document.getElementById(toolbarContainerId)).toBeNull();
+});
diff --git a/packages/browser-sdk/test/cleanupUi.ts b/packages/browser-sdk/test/cleanupUi.ts
new file mode 100644
index 000000000..387180d99
--- /dev/null
+++ b/packages/browser-sdk/test/cleanupUi.ts
@@ -0,0 +1,16 @@
+import { render } from "preact";
+
+import { feedbackContainerId, toolbarContainerId } from "../src/ui/constants";
+
+/** Unmount Preact before removing its hosts or tearing down jsdom globals. */
+export function cleanupUi() {
+  if (typeof document === "undefined") return;
+
+  for (const id of [feedbackContainerId, toolbarContainerId]) {
+    const host = document.getElementById(id);
+    if (host?.shadowRoot) {
+      render(null, host.shadowRoot);
+    }
+    host?.remove();
+  }
+}
diff --git a/packages/browser-sdk/test/usage.test.ts b/packages/browser-sdk/test/usage.test.ts
index 86879005d..44e001f70 100644
--- a/packages/browser-sdk/test/usage.test.ts
+++ b/packages/browser-sdk/test/usage.test.ts
@@ -37,9 +37,6 @@ const clientNotInitializedError = {
 };
 
 vi.mock("../src/sse");
-// These tests cover SDK usage, not toolbar rendering. Avoid scheduling Preact
-// renders that can outlive the test's browser environment.
-vi.mock("../src/toolbar", () => ({ showToolbarToggle: vi.fn() }));
 vi.mock("../src/feedback/promptStorage", () => {
   return {
     markPromptMessageCompleted: vi.fn(),
diff --git a/packages/browser-sdk/vitest.setup.ts b/packages/browser-sdk/vitest.setup.ts
index 9161f5f54..92decc881 100644
--- a/packages/browser-sdk/vitest.setup.ts
+++ b/packages/browser-sdk/vitest.setup.ts
@@ -1,5 +1,6 @@
 import { afterAll, afterEach, beforeAll } from "vitest";
 
+import { cleanupUi } from "./test/cleanupUi";
 import { server } from "./test/mocks/server.js";
 
 beforeAll(() => {
@@ -11,6 +12,7 @@ beforeAll(() => {
 });
 
 afterEach(() => {
+  cleanupUi();
   server.resetHandlers();
 });