diff --git a/packages/react-aria-components/test/DateField.browser.test.tsx b/packages/react-aria-components/test/DateField.browser.test.tsx
new file mode 100644
index 00000000000..0e99552fc92
--- /dev/null
+++ b/packages/react-aria-components/test/DateField.browser.test.tsx
@@ -0,0 +1,79 @@
+/*
+ * Copyright 2026 Adobe. All rights reserved.
+ * This file is licensed to you under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License. You may obtain a copy
+ * of the License at http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under
+ * the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR REPRESENTATIONS
+ * OF ANY KIND, either express or implied. See the License for the specific language
+ * governing permissions and limitations under the License.
+ */
+
+import {afterEach, expect, it, vi} from 'vitest';
+import {CalendarDate} from '@internationalized/date';
+import {DateField, DateInput, DateSegment} from '../src/DateField';
+import React from 'react';
+import {render} from 'vitest-browser-react';
+import {userEvent} from 'vitest/browser';
+
+function DateFieldWithSibling() {
+  return (
+    <>
+      <button type="button" data-testid="sibling">
+        sibling
+      </button>
+      <DateField aria-label="date" defaultValue={new CalendarDate(2020, 2, 3)}>
+        <DateInput>{segment => <DateSegment segment={segment} />}</DateInput>
+      </DateField>
+    </>
+  );
+}
+
+afterEach(() => {
+  vi.restoreAllMocks();
+});
+
+// Regression test for a Firefox-only focus steal. useDateSegment installs a document-level
+// 'selectionchange' listener that re-collapses the window selection onto the segment whenever the
+// selection anchor is inside it. In Firefox the caret inside a sibling <input> is not reflected in
+// the document selection, so a stale anchor remains parked in a segment after focus moves away;
+// collapsing onto the contentEditable segment there steals focus back into it (e.g. while typing
+// in a neighbouring input). The fix gates the collapse on the segment being the active element.
+// See https://github.com/adobe/react-spectrum/issues/10259
+//
+// The natural reproduction is Firefox-specific and impossible to set up faithfully through the
+// test harness: in Chromium/WebKit focusing another element collapses the document selection, so
+// the stale anchor never survives, and re-parking the real selection onto the contentEditable
+// segment triggers the very focus steal we're guarding against. Instead we reproduce the guarded
+// precondition deterministically — a selection anchored inside the segment while a *different*
+// element genuinely holds focus — by stubbing window.getSelection for the single selectionchange,
+// and assert on the guarded behaviour itself: the handler must not collapse the selection onto the
+// segment. This fails in every browser without the fix.
+it('does not collapse the selection onto a date segment while another element is focused', async () => {
+  let {container} = await render(<DateFieldWithSibling />);
+
+  let button = container.querySelector('[data-testid="sibling"]') as HTMLButtonElement;
+  let segments = [...container.querySelectorAll('[role="spinbutton"]')] as HTMLElement[];
+  let lastSegment = segments[segments.length - 1];
+
+  // Genuinely move focus to a sibling element, so getActiveElement() !== the segment.
+  await userEvent.click(button);
+  expect(document.activeElement).toBe(button);
+
+  // Present the Firefox state: a stale selection anchor still inside the segment. Stubbing
+  // window.getSelection keeps real focus untouched (collapsing onto the contentEditable segment
+  // for real would itself steal focus on Firefox, defeating the setup).
+  let collapse = vi.fn();
+  let staleSelection = {
+    anchorNode: lastSegment.firstChild ?? lastSegment,
+    collapse
+  } as unknown as Selection;
+  vi.spyOn(window, 'getSelection').mockReturnValue(staleSelection);
+
+  document.dispatchEvent(new Event('selectionchange'));
+
+  // Without the fix the handler calls selection.collapse(segment) here — the focus steal on Firefox.
+  expect(collapse).not.toHaveBeenCalled();
+  expect(document.activeElement).toBe(button);
+});
diff --git a/packages/react-aria/src/datepicker/useDateSegment.ts b/packages/react-aria/src/datepicker/useDateSegment.ts
index 9119e2b7d76..f2db9783f4e 100644
--- a/packages/react-aria/src/datepicker/useDateSegment.ts
+++ b/packages/react-aria/src/datepicker/useDateSegment.ts
@@ -264,7 +264,15 @@ export function useDateSegment(
     // Otherwise, when tapping on a segment in Android Chrome and then entering text,
     // composition events will be fired that break the DOM structure and crash the page.
     let selection = window.getSelection();
-    if (selection?.anchorNode && nodeContains(ref.current, selection?.anchorNode)) {
+    // Only collapse while this segment is actually focused. In Firefox, the selection inside a
+    // sibling text input is not reflected in the document selection, so a stale anchor can remain
+    // inside a segment after focus moves away; collapsing onto the contentEditable segment there
+    // steals focus back into it (e.g. while typing in a neighbouring input). See #10259.
+    if (
+      selection?.anchorNode &&
+      nodeContains(ref.current, selection?.anchorNode) &&
+      getActiveElement() === ref.current
+    ) {
       selection.collapse(ref.current);
     }
   });