diff --git a/frontend/src/views/user/CustomPageView.vue b/frontend/src/views/user/CustomPageView.vue
index 8006695dda..10ddceb479 100644
--- a/frontend/src/views/user/CustomPageView.vue
+++ b/frontend/src/views/user/CustomPageView.vue
@@ -94,12 +94,21 @@
         </div>
 
         <!-- Iframe embed mode -->
-        <div v-else class="custom-embed-shell">
+        <div v-else ref="embedShell" class="custom-embed-shell">
           <a
+            ref="openButton"
             :href="embeddedUrl"
             target="_blank"
             rel="noopener noreferrer"
             class="btn btn-secondary btn-sm custom-open-fab"
+            :style="openButtonPosition ? { left: `${openButtonPosition.x}px`, top: `${openButtonPosition.y}px`, right: 'auto' } : undefined"
+            @pointerdown="startButtonDrag"
+            @pointermove="moveButtonDrag"
+            @pointerup="endButtonDrag"
+            @pointercancel="endButtonDrag"
+            @lostpointercapture="endButtonDrag"
+            @dragstart.prevent
+            @click="handleOpenButtonClick"
           >
             <Icon name="externalLink" size="sm" class="mr-1.5" :stroke-width="2" />
             {{ t('customPage.openInNewTab') }}
@@ -118,6 +127,7 @@
 <script setup lang="ts">
 import { computed, nextTick, onMounted, onUnmounted, ref, watch } from 'vue'
 import { useRoute } from 'vue-router'
+import { useResizeObserver } from '@vueuse/core'
 import { useI18n } from 'vue-i18n'
 import { useAppStore } from '@/stores'
 import { useAuthStore } from '@/stores/auth'
@@ -150,6 +160,63 @@ const tocVisible = ref(typeof window !== 'undefined' ? window.innerWidth > 768 :
 const activeHeadingId = ref('')
 let themeObserver: MutationObserver | null = null
 
+const embedShell = ref<HTMLElement | null>(null)
+const openButton = ref<HTMLAnchorElement | null>(null)
+const openButtonPosition = ref<{ x: number; y: number } | null>(null)
+let buttonDrag: { pointerId: number; startX: number; startY: number; x: number; y: number } | null = null
+let suppressButtonClick = false
+
+function setOpenButtonPosition(x: number, y: number) {
+  const shell = embedShell.value
+  const button = openButton.value
+  if (!shell || !button) return
+  openButtonPosition.value = {
+    x: Math.max(0, Math.min(x, shell.clientWidth - button.offsetWidth)),
+    y: Math.max(0, Math.min(y, shell.clientHeight - button.offsetHeight)),
+  }
+}
+
+function startButtonDrag(event: PointerEvent) {
+  if (event.button !== 0 || !event.isPrimary || !openButton.value) return
+  const button = openButton.value
+  suppressButtonClick = false
+  buttonDrag = {
+    pointerId: event.pointerId, startX: event.clientX, startY: event.clientY,
+    x: button.offsetLeft, y: button.offsetTop,
+  }
+  // Capture keeps receiving moves when the pointer crosses the embedded iframe.
+  button.setPointerCapture(event.pointerId)
+}
+
+function moveButtonDrag(event: PointerEvent) {
+  if (!buttonDrag || event.pointerId !== buttonDrag.pointerId) return
+  const dx = event.clientX - buttonDrag.startX
+  const dy = event.clientY - buttonDrag.startY
+  if (!suppressButtonClick && Math.hypot(dx, dy) < 4) return
+  suppressButtonClick = true
+  setOpenButtonPosition(buttonDrag.x + dx, buttonDrag.y + dy)
+  event.preventDefault()
+}
+
+function endButtonDrag(event: PointerEvent) {
+  if (!buttonDrag || event.pointerId !== buttonDrag.pointerId) return
+  buttonDrag = null
+  if (openButton.value?.hasPointerCapture(event.pointerId)) {
+    openButton.value.releasePointerCapture(event.pointerId)
+  }
+}
+
+function handleOpenButtonClick(event: MouseEvent) {
+  if (suppressButtonClick && event.detail !== 0) event.preventDefault()
+  suppressButtonClick = false
+}
+
+useResizeObserver([embedShell, openButton], () => {
+  if (openButtonPosition.value) {
+    setOpenButtonPosition(openButtonPosition.value.x, openButtonPosition.value.y)
+  }
+})
+
 const menuItemId = computed(() => route.params.id as string)
 
 const menuItem = computed(() => {
@@ -445,7 +512,7 @@ onUnmounted(() => {
 }
 
 .custom-open-fab {
-  @apply absolute right-3 top-3 z-10;
+  @apply absolute right-3 top-3 z-10 w-max max-w-full touch-none select-none transition-colors;
   @apply shadow-sm backdrop-blur supports-[backdrop-filter]:bg-white/80 dark:supports-[backdrop-filter]:bg-dark-800/80;
 }
 
diff --git a/frontend/src/views/user/__tests__/CustomPageView.spec.ts b/frontend/src/views/user/__tests__/CustomPageView.spec.ts
new file mode 100644
index 0000000000..37b790d0b7
--- /dev/null
+++ b/frontend/src/views/user/__tests__/CustomPageView.spec.ts
@@ -0,0 +1,161 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+import { flushPromises, mount } from '@vue/test-utils'
+import { nextTick } from 'vue'
+import CustomPageView from '../CustomPageView.vue'
+
+const { appStore } = vi.hoisted(() => ({
+  appStore: {
+    publicSettingsLoaded: true,
+    cachedPublicSettings: { custom_menu_items: [{ id: 'docs', url: 'https://example.com/docs' }] },
+  },
+}))
+
+vi.mock('@/components/layout/AppLayout.vue', () => ({ default: { template: '<div><slot /></div>' } }))
+vi.mock('vue-router', () => ({ useRoute: () => ({ params: { id: 'docs' } }) }))
+vi.mock('vue-i18n', () => ({ useI18n: () => ({ t: (key: string) => key, locale: { value: 'en' } }) }))
+vi.mock('@/stores', () => ({ useAppStore: () => appStore }))
+vi.mock('@/stores/auth', () => ({ useAuthStore: () => ({ isAdmin: false, user: { id: 7 }, token: 'test-token' }) }))
+vi.mock('@/stores/adminSettings', () => ({ useAdminSettingsStore: () => ({ customMenuItems: [] }) }))
+vi.mock('@/api/client', () => ({ buildApiUrl: (path: string) => `/api/v1${path}` }))
+
+let notifyResize: () => void
+const wrappers: ReturnType<typeof mount>[] = []
+
+function mountPage() {
+  const wrapper = mount(CustomPageView, {
+    global: { stubs: { AppLayout: { template: '<div><slot /></div>' }, Icon: true } },
+  })
+  wrappers.push(wrapper)
+  return wrapper
+}
+
+function mountEmbed() {
+  const wrapper = mountPage()
+  const shell = wrapper.get('.custom-embed-shell').element
+  const button = wrapper.get<HTMLAnchorElement>('.custom-open-fab').element
+  const size = { width: 800, height: 600 }
+  let capturedPointer: number | null = null
+  Object.defineProperties(shell, {
+    clientWidth: { get: () => size.width }, clientHeight: { get: () => size.height },
+  })
+  Object.defineProperties(button, {
+    offsetWidth: { value: 100 }, offsetHeight: { value: 32 },
+    offsetLeft: { get: () => Number.parseFloat(button.style.left || '688') },
+    offsetTop: { get: () => Number.parseFloat(button.style.top || '12') },
+    setPointerCapture: { value: vi.fn((id: number) => { capturedPointer = id }) },
+    hasPointerCapture: { value: (id: number) => capturedPointer === id },
+    releasePointerCapture: { value: vi.fn(() => { capturedPointer = null }) },
+  })
+  return { wrapper, button, size }
+}
+
+async function pointer(button: HTMLElement, type: string, x: number, y: number, extra = {}) {
+  const event = new MouseEvent(type, { clientX: x, clientY: y, bubbles: true, cancelable: true, ...extra })
+  Object.defineProperties(event, {
+    pointerId: { value: 1 }, isPrimary: { value: true },
+  })
+  button.dispatchEvent(event)
+  await nextTick()
+}
+
+function click(button: HTMLElement, detail = 1) {
+  const event = new MouseEvent('click', { bubbles: true, cancelable: true, detail })
+  button.dispatchEvent(event)
+  return event
+}
+
+describe('custom page open button', () => {
+  beforeEach(() => {
+    appStore.cachedPublicSettings.custom_menu_items = [{ id: 'docs', url: 'https://example.com/docs' }]
+    vi.stubGlobal('ResizeObserver', class {
+      constructor(callback: () => void) { notifyResize = callback }
+      observe() {}
+      disconnect() {}
+    })
+  })
+
+  afterEach(() => {
+    wrappers.splice(0).forEach(wrapper => wrapper.unmount())
+    vi.unstubAllGlobals()
+  })
+
+  it('preserves the embedded URL, secure link attributes, and normal clicks with small pointer movements', async () => {
+    const { wrapper, button } = mountEmbed()
+    expect(button.href).toBe(wrapper.get('iframe').attributes('src'))
+    expect(button.href).toContain('user_id=7')
+    expect(button.href).toContain('token=test-token')
+    expect(button.target).toBe('_blank')
+    expect(button.rel).toBe('noopener noreferrer')
+    await pointer(button, 'pointerdown', 700, 24)
+    await pointer(button, 'pointermove', 702, 25)
+    await pointer(button, 'pointerup', 702, 25)
+    expect(button.style.left).toBe('')
+    expect(click(button).defaultPrevented).toBe(false)
+    expect(click(button, 0).defaultPrevented).toBe(false)
+  })
+
+  it('captures the pointer across iframe content and suppresses only the click following a drag', async () => {
+    const { button } = mountEmbed()
+    await pointer(button, 'pointerdown', 700, 24)
+    expect(button.setPointerCapture).toHaveBeenCalledWith(1)
+    await pointer(button, 'pointermove', 200, 124)
+    expect(button.style.left).toBe('188px')
+    expect(button.style.top).toBe('112px')
+    await pointer(button, 'pointerup', 200, 124)
+    expect(button.releasePointerCapture).toHaveBeenCalledWith(1)
+    expect(click(button).defaultPrevented).toBe(true)
+    expect(click(button).defaultPrevented).toBe(false)
+    await pointer(button, 'pointerdown', 200, 124)
+    await pointer(button, 'pointermove', 220, 124)
+    await pointer(button, 'pointerup', 220, 124)
+    expect(click(button, 0).defaultPrevented).toBe(false)
+  })
+
+  it('keeps the button inside each boundary and reachable when the container shrinks', async () => {
+    const { button, size } = mountEmbed()
+    await pointer(button, 'pointerdown', 700, 24)
+    await pointer(button, 'pointermove', -1000, -1000)
+    expect([button.style.left, button.style.top]).toEqual(['0px', '0px'])
+    await pointer(button, 'pointermove', 2000, 2000)
+    expect([button.style.left, button.style.top]).toEqual(['700px', '568px'])
+    await pointer(button, 'pointerup', 2000, 2000)
+    size.width = 300
+    size.height = 200
+    notifyResize()
+    await nextTick()
+    expect([button.style.left, button.style.top]).toEqual(['200px', '168px'])
+  })
+
+  it('stops moving on cancellation or lost pointer capture and permits the next normal click', async () => {
+    const { button } = mountEmbed()
+    for (const endEvent of ['pointercancel', 'lostpointercapture']) {
+      await pointer(button, 'pointerdown', 700, 24)
+      await pointer(button, 'pointermove', 500, 124)
+      await pointer(button, endEvent, 500, 124)
+      const position = button.style.cssText
+      await pointer(button, 'pointermove', 400, 224)
+      expect(button.style.cssText).toBe(position)
+      await pointer(button, 'pointerdown', 500, 124)
+      await pointer(button, 'pointerup', 500, 124)
+      expect(click(button).defaultPrevented).toBe(false)
+    }
+  })
+
+  it('leaves secondary mouse button gestures alone', async () => {
+    const { button } = mountEmbed()
+    await pointer(button, 'pointerdown', 700, 24, { button: 2 })
+    await pointer(button, 'pointermove', 500, 124)
+    expect(button.setPointerCapture).not.toHaveBeenCalled()
+    expect(button.style.left).toBe('')
+  })
+
+  it('keeps Markdown pages separate from the embedded-page controls', async () => {
+    appStore.cachedPublicSettings.custom_menu_items = [{ id: 'docs', url: 'md:guide' }]
+    vi.stubGlobal('fetch', vi.fn().mockResolvedValue({ ok: true, text: async () => '# Guide' }))
+    const wrapper = mountPage()
+    await flushPromises()
+    expect(wrapper.find('.custom-open-fab').exists()).toBe(false)
+    expect(wrapper.find('iframe').exists()).toBe(false)
+    expect(wrapper.get('.markdown-page-content h1').text()).toBe('Guide')
+  })
+})