diff --git a/.github/instructions/frontend-test.instructions.md b/.github/instructions/frontend-test.instructions.md
index d051329ae5..c74b7cea95 100644
--- a/.github/instructions/frontend-test.instructions.md
+++ b/.github/instructions/frontend-test.instructions.md
@@ -325,6 +325,10 @@ The following are already mocked globally in `src/setupTests.ts` — do NOT re-m
 - `Element.prototype.scrollTo` / `scrollIntoView`
 - `URL.createObjectURL` / `revokeObjectURL`
 - `import.meta.env` variables (`VITE_API_URL`, `MODE`)
+- JSDOM focus layout (`offsetParent` and viewport-sized body bounds). Disconnected elements and `display: none` ancestors have no simulated layout; visibility and disabled checks remain intact. This does not simulate positioning or actual dimensions.
+
+For modal timer regressions, use fake timers with `userEvent.setup({ advanceTimers: jest.advanceTimersByTime })` and advance timers inside `act`. Keep normal accessible-role queries; querying hidden dialogs or extending timeouts can mask focus-management failures.
+After navigating from a modal, wait for an accessible element on the destination page, not just a test ID. Restoring background accessibility is also deferred.
 
 ## What to Test
 
diff --git a/frontend/src/components/Configuration/Configuration.test.tsx b/frontend/src/components/Configuration/Configuration.test.tsx
index 9d56c837e7..5ecbfeda43 100644
--- a/frontend/src/components/Configuration/Configuration.test.tsx
+++ b/frontend/src/components/Configuration/Configuration.test.tsx
@@ -1,7 +1,7 @@
 import type { ReactElement } from 'react'
 
 import { FluentProvider, webLightTheme } from '@fluentui/react-components'
-import { fireEvent, render, screen, waitFor, within } from '@testing-library/react'
+import { act, cleanup, render, screen, waitFor, within } from '@testing-library/react'
 import userEvent from '@testing-library/user-event'
 import { MemoryRouter, useLocation, useNavigate } from 'react-router'
 
@@ -29,9 +29,6 @@ jest.mock('@/services/api', () => ({
 const mockedConfigurationApi = jest.mocked(configurationApi)
 const mockedInitializersApi = jest.mocked(initializersApi)
 
-// Fluent UI dialogs can render slowly in JSDOM under full test load.
-jest.setTimeout(60_000)
-
 function RouterProbe(): ReactElement {
   const location = useLocation()
   const navigate = useNavigate()
@@ -228,20 +225,10 @@ describe('Configuration', () => {
       { selector: 'label' },
     )).toBeInTheDocument()
     await user.click(screen.getByRole('button', { name: 'Add initializer' }))
-    const dialog = await screen.findByRole(
-      'dialog',
-      { name: 'Add custom initializer' },
-      { timeout: 15_000 },
-    )
-    const nameInput = await within(dialog).findByRole(
-      'textbox',
-      { name: /Initializer name/ },
-      { timeout: 15_000 },
-    )
+    const dialog = await screen.findByRole('dialog', { name: 'Add custom initializer' })
+    const nameInput = within(dialog).getByRole('textbox', { name: /Initializer name/ })
     await user.type(nameInput, 'new_custom')
-    fireEvent.change(within(dialog).getByRole('textbox', { name: 'Python source' }), {
-      target: { value: 'class NewCustom: pass' },
-    })
+    await user.type(within(dialog).getByRole('textbox', { name: 'Python source' }), 'class NewCustom: pass')
     await user.click(within(dialog).getByRole('button', { name: 'Add' }))
 
     await waitFor(() => {
@@ -252,6 +239,36 @@ describe('Configuration', () => {
     })
   })
 
+  it('should keep the add initializer dialog accessible after modal housekeeping', async () => {
+    jest.useFakeTimers()
+    try {
+      const user = userEvent.setup({ advanceTimers: jest.advanceTimersByTime })
+      renderPage()
+
+      await user.click(screen.getByRole('tab', { name: 'Custom Initializers' }))
+      expect(await screen.findByText(
+        'C:/Users/test/.pyrit/custom_initializers/custom_target.py',
+        { selector: 'label' },
+      )).toBeInTheDocument()
+      await user.click(screen.getByRole('button', { name: 'Add initializer' }))
+
+      // Tabster defers its modal aria-hidden update by 250 ms.
+      await act(async () => {
+        jest.advanceTimersByTime(250)
+      })
+
+      const dialog = screen.getByRole('dialog', { name: 'Add custom initializer' })
+      expect(within(dialog).getByRole('textbox', { name: /Initializer name/ })).toHaveFocus()
+      expect(within(dialog).getByRole('button', { name: 'Add' })).toBeDisabled()
+      await user.click(within(dialog).getByRole('button', { name: 'Cancel' }))
+      expect(screen.queryByRole('dialog', { name: 'Add custom initializer' })).not.toBeInTheDocument()
+    } finally {
+      cleanup()
+      jest.runOnlyPendingTimers()
+      jest.useRealTimers()
+    }
+  })
+
   it('should show configured initializers without a runtime apply action', async () => {
     const user = userEvent.setup()
     renderPage()
diff --git a/frontend/src/components/Scenarios/ScenarioFlow.test.tsx b/frontend/src/components/Scenarios/ScenarioFlow.test.tsx
index 5f9f4dc9a0..b313537696 100644
--- a/frontend/src/components/Scenarios/ScenarioFlow.test.tsx
+++ b/frontend/src/components/Scenarios/ScenarioFlow.test.tsx
@@ -200,7 +200,7 @@ describe('Scenario catalog-to-run integration', () => {
     expect(within(estimate).getByText('Total atomic attacks').parentElement).toHaveTextContent('2')
 
     await user.click(screen.getByTestId('launch-scenario-btn'))
-    const preview = await screen.findByRole('dialog', { hidden: true })
+    const preview = await screen.findByRole('dialog', { name: 'Run preview' })
     await user.click(within(preview).getByTestId('confirm-launch-scenario-btn'))
 
     await waitFor(() => expect(mockStartRun).toHaveBeenCalledWith({
@@ -216,6 +216,6 @@ describe('Scenario catalog-to-run integration', () => {
     expect(screen.getByLabelText('Current route')).toHaveTextContent(
       `/scanner-history/${RUN_ID}`,
     )
-    expect(screen.getByRole('heading', { level: 1, name: SCENARIO_NAME })).toBeInTheDocument()
+    expect(await screen.findByRole('heading', { level: 1, name: SCENARIO_NAME })).toBeInTheDocument()
   })
 })
diff --git a/frontend/src/setupTests.test.tsx b/frontend/src/setupTests.test.tsx
new file mode 100644
index 0000000000..e272a24fb6
--- /dev/null
+++ b/frontend/src/setupTests.test.tsx
@@ -0,0 +1,87 @@
+import type { CSSProperties } from 'react'
+
+import { Dialog, DialogSurface, FluentProvider, webLightTheme } from '@fluentui/react-components'
+import { render, screen } from '@testing-library/react'
+import userEvent from '@testing-library/user-event'
+
+describe('JSDOM focus layout', () => {
+  beforeEach(() => {
+    jest.clearAllMocks()
+  })
+
+  it('should provide layout for displayed controls', () => {
+    render(<button type="button">Visible control</button>)
+
+    expect(screen.getByRole('button', { name: 'Visible control' }).offsetParent).not.toBeNull()
+    expect(document.body.getBoundingClientRect().width).toBe(window.innerWidth)
+    expect(document.body.getBoundingClientRect().height).toBe(window.innerHeight)
+  })
+
+  it('should not provide layout for detached controls', () => {
+    const button = document.createElement('button')
+
+    expect(button.offsetParent).toBeNull()
+  })
+
+  it('should not provide layout for hidden controls or their descendants', () => {
+    render(
+      <>
+        <button type="button" hidden>Hidden control</button>
+        <div hidden><button type="button">Hidden descendant</button></div>
+      </>,
+    )
+
+    expect(screen.getByText('Hidden control').offsetParent).toBeNull()
+    expect(screen.getByText('Hidden descendant').offsetParent).toBeNull()
+    expect(screen.queryByRole('button')).not.toBeInTheDocument()
+  })
+
+  it.each<CSSProperties>([
+    { display: 'none' },
+    { visibility: 'hidden' },
+  ])('should preserve CSS-hidden controls (%j)', (style: CSSProperties) => {
+    render(<div style={style}><button type="button">CSS-hidden control</button></div>)
+
+    expect(screen.queryByRole('button', { name: 'CSS-hidden control' })).not.toBeInTheDocument()
+    if (style.display === 'none') {
+      expect(screen.getByText('CSS-hidden control').offsetParent).toBeNull()
+    }
+  })
+
+  it('should preserve fixed positioning and disabled controls', async () => {
+    const user = userEvent.setup()
+    render(
+      <>
+        <button type="button" style={{ position: 'fixed' }}>Fixed control</button>
+        <button type="button" disabled>Disabled control</button>
+      </>,
+    )
+
+    const fixedButton = screen.getByRole('button', { name: 'Fixed control' })
+    const disabledButton = screen.getByRole('button', { name: 'Disabled control' })
+    expect(fixedButton.offsetParent).toBeNull()
+    expect(disabledButton).toBeDisabled()
+    await user.click(disabledButton)
+    expect(disabledButton).not.toHaveFocus()
+  })
+
+  it('should focus only visible, enabled dialog controls', () => {
+    render(
+      <FluentProvider theme={webLightTheme}>
+        <Dialog open>
+          <DialogSurface aria-label="Focus test">
+            <button type="button" hidden>Hidden control</button>
+            <div style={{ display: 'none' }}><button type="button">Hidden descendant</button></div>
+            <div style={{ visibility: 'hidden' }}><button type="button">Invisible descendant</button></div>
+            <button type="button" aria-hidden="true">Accessibility-hidden control</button>
+            <button type="button" disabled>Disabled control</button>
+            <fieldset disabled><button type="button">Disabled descendant</button></fieldset>
+            <button type="button">Available control</button>
+          </DialogSurface>
+        </Dialog>
+      </FluentProvider>,
+    )
+
+    expect(screen.getByRole('button', { name: 'Available control' })).toHaveFocus()
+  })
+})
diff --git a/frontend/src/setupTests.ts b/frontend/src/setupTests.ts
index 8ad475b685..36acf3ed6c 100644
--- a/frontend/src/setupTests.ts
+++ b/frontend/src/setupTests.ts
@@ -2,8 +2,7 @@ import "@testing-library/jest-dom";
 import { configure } from "@testing-library/react";
 import { TextEncoder, TextDecoder } from "util";
 
-// Give async queries a little more headroom than the 1s default: Fluent modal
-// dialogs (tabster modalizer + Textarea) can take longer to mount under load.
+// Give async data and rendering assertions headroom under parallel test load.
 configure({ asyncUtilTimeout: 5000 });
 
 // jsdom omits TextEncoder/TextDecoder, which react-router references at
@@ -18,6 +17,35 @@ process.env.MODE = "test";
 process.env.DEV = "true";
 process.env.PROD = "false";
 
+function isDisplayed(element: HTMLElement): boolean {
+  if (!element.isConnected) {
+    return false;
+  }
+  for (let ancestor: HTMLElement | null = element; ancestor; ancestor = ancestor.parentElement) {
+    if (getComputedStyle(ancestor).display === "none") {
+      return false;
+    }
+  }
+  return true;
+}
+
+// JSDOM has no layout. Without these boxes, Tabster cannot focus dialog controls
+// and can mark the focused dialog surface aria-hidden on its deferred update.
+Object.defineProperty(HTMLElement.prototype, "offsetParent", {
+  configurable: true,
+  get(this: HTMLElement): Element | null {
+    if (!isDisplayed(this) || this === document.body || getComputedStyle(this).position === "fixed") {
+      return null;
+    }
+    return this.parentElement;
+  },
+});
+
+document.body.getBoundingClientRect = (): DOMRect =>
+  isDisplayed(document.body)
+    ? new DOMRect(0, 0, window.innerWidth, window.innerHeight)
+    : new DOMRect();
+
 // Mock window.matchMedia for Fluent UI components
 Object.defineProperty(window, "matchMedia", {
   writable: true,