diff --git a/.github/workflows/nightly.yml b/.github/workflows/nightly.yml
index 8731eb8a84..8a6ccfeb6b 100644
--- a/.github/workflows/nightly.yml
+++ b/.github/workflows/nightly.yml
@@ -41,6 +41,11 @@ jobs:
       - name: Install all Playwright browsers
         run: task e2e:install
 
+      - name: Build frontend (production bundle for vite preview)
+        env:
+          VITE_BUILD_FOR_PREVIEW: "1"
+        run: task frontend:build
+
       - name: Run E2E tests (all browsers)
         run: task e2e:cross-browser
 
diff --git a/frontend/editor/src/core/tests/helpers/ui-helpers.ts b/frontend/editor/src/core/tests/helpers/ui-helpers.ts
index 7c08f93f60..cea44eabb5 100644
--- a/frontend/editor/src/core/tests/helpers/ui-helpers.ts
+++ b/frontend/editor/src/core/tests/helpers/ui-helpers.ts
@@ -37,10 +37,9 @@ export async function waitForModalClose(
 }
 
 /**
- * Upload one or more files through the FileSidebar's "Open from computer"
- * action. The button is always rendered (collapsed or expanded sidebar) and
- * triggers the hidden `data-testid="file-input"` native picker directly -
- * there is no modal to wait for under the post-refactor design.
+ * Upload one or more files through the FileSidebar's hidden native input.
+ * The sidebar button is still the user-facing entry point, but tests drive
+ * the input directly to avoid Firefox file-picker side effects.
  *
  * `setInputFiles` doesn't await the input's async onChange (which writes to
  * IndexedDB via `addFiles`), so without a sync point a caller that follows
@@ -53,7 +52,6 @@ export async function uploadFiles(
   filePaths: string | string[],
 ): Promise<void> {
   const paths = Array.isArray(filePaths) ? filePaths : [filePaths];
-  await page.getByTestId("files-button").click();
   await page.locator('[data-testid="file-input"]').setInputFiles(paths);
   // Sync point: wait until at least one file lands in the sidebar's file
   // list. The list only renders once `addFiles` has resolved (which awaits
@@ -66,16 +64,19 @@ export async function uploadFiles(
 /**
  * Some tools (Merge in particular) park the workbench in `viewer` mode after
  * upload, which keeps the run button disabled. The UI exposes a "Go to file
- * editor" affordance to switch out of viewer mode; this helper clicks it
- * when present and is a no-op otherwise.
+ * editor" affordance to switch out of viewer mode; this helper clicks the
+ * file-editor segment when present and is a no-op otherwise.
  */
 export async function switchToEditorIfViewerMode(page: Page): Promise<void> {
-  const goToEditor = page.getByRole("button", {
-    name: /go to file editor/i,
-  });
-  if (await goToEditor.isVisible({ timeout: 1_000 }).catch(() => false)) {
-    await goToEditor.click();
+  const viewSwitcher = page.locator('[data-tour="view-switcher"]');
+  const viewButtons = viewSwitcher.getByRole("button");
+  const buttonCount = await viewButtons.count().catch(() => 0);
+  if (buttonCount < 2) {
+    return;
   }
+
+  // The file-editor option is the last segment in the shared switcher.
+  await viewButtons.last().click({ timeout: 1_000 });
 }
 
 /**
diff --git a/frontend/editor/src/core/tests/live/encrypted-unlock-then-tool.spec.ts b/frontend/editor/src/core/tests/live/encrypted-unlock-then-tool.spec.ts
index ef03c54369..512e71dc06 100644
--- a/frontend/editor/src/core/tests/live/encrypted-unlock-then-tool.spec.ts
+++ b/frontend/editor/src/core/tests/live/encrypted-unlock-then-tool.spec.ts
@@ -31,7 +31,6 @@ test.describe("Encrypted PDF: unlock then merge", () => {
     await page.goto("/merge");
     await page.waitForLoadState("domcontentloaded");
 
-    await page.getByTestId("files-button").click();
     await page
       .locator('[data-testid="file-input"]')
       .setInputFiles([ENCRYPTED_PDF, SAMPLE_PDF]);
diff --git a/frontend/editor/src/core/tests/stubbed/certificate-validation.spec.ts b/frontend/editor/src/core/tests/stubbed/certificate-validation.spec.ts
index 1f8886bab4..09df086fc2 100644
--- a/frontend/editor/src/core/tests/stubbed/certificate-validation.spec.ts
+++ b/frontend/editor/src/core/tests/stubbed/certificate-validation.spec.ts
@@ -1,5 +1,10 @@
 import { test, expect, type Page } from "@playwright/test";
 import path from "path";
+import {
+  mockAppApis,
+  seedCookieConsent,
+  skipOnboarding,
+} from "@app/tests/helpers/api-stubs";
 
 // ---------------------------------------------------------------------------
 // Test fixtures — pre-generated keystores in test-fixtures/certs/
@@ -77,17 +82,10 @@ async function selectCertType(page: Page, label: string) {
 }
 
 // ---------------------------------------------------------------------------
-// Helper: upload a file into the Mantine <FileInput> (hidden native input)
+// Helper: upload a file into the Mantine <FileInput> via the hidden native input.
 // ---------------------------------------------------------------------------
 async function uploadCertFile(page: Page, filePath: string) {
-  // Mantine FileInput uses a visually hidden <input type="file">.
-  // We click the visible button to expose it, then set files via the hidden input.
-  const certFileInput = page.getByTestId("cert-file-input");
-  await certFileInput.click();
-  // After click, the file chooser or the hidden input becomes interactive.
-  // Use the first file input on the page (Mantine places it near the button).
-  const fileInput = page.locator('input[type="file"]').first();
-  await fileInput.setInputFiles(filePath);
+  await page.locator('input[type="file"]').first().setInputFiles(filePath);
 }
 
 // ---------------------------------------------------------------------------
@@ -95,6 +93,9 @@ async function uploadCertFile(page: Page, filePath: string) {
 // ---------------------------------------------------------------------------
 test.describe("Certificate Validation — ParticipantView", () => {
   test.beforeEach(async ({ page }) => {
+    await seedCookieConsent(page);
+    await skipOnboarding(page);
+    await mockAppApis(page);
     await mockParticipantApis(page);
   });
 
diff --git a/frontend/editor/src/core/tests/stubbed/convert.spec.ts b/frontend/editor/src/core/tests/stubbed/convert.spec.ts
index cd6a60884a..adf30800f2 100644
--- a/frontend/editor/src/core/tests/stubbed/convert.spec.ts
+++ b/frontend/editor/src/core/tests/stubbed/convert.spec.ts
@@ -23,13 +23,11 @@ async function dismissTourTooltip(page: Page) {
 }
 
 // ---------------------------------------------------------------------------
-// Helper: upload a file via the FileSidebar's "Open from computer" action.
-// The button now triggers the native OS picker directly - no modal - and
-// the hidden `data-testid="file-input"` accepts `setInputFiles` in either
-// sidebar state.
+// Helper: upload a file via the FileSidebar's hidden native input.
+// This avoids native file-picker side effects in Firefox while still
+// exercising the same upload path.
 // ---------------------------------------------------------------------------
 async function uploadFile(page: Page, filePath: string) {
-  await page.getByTestId("files-button").click();
   await page.locator('[data-testid="file-input"]').setInputFiles(filePath);
 }
 
diff --git a/frontend/editor/src/core/tests/stubbed/encrypted-pdf-unlock.spec.ts b/frontend/editor/src/core/tests/stubbed/encrypted-pdf-unlock.spec.ts
index 7e220a3bda..d888c99ed0 100644
--- a/frontend/editor/src/core/tests/stubbed/encrypted-pdf-unlock.spec.ts
+++ b/frontend/editor/src/core/tests/stubbed/encrypted-pdf-unlock.spec.ts
@@ -63,8 +63,7 @@ function mockRemovePasswordWrongPassword(page: Page) {
 }
 
 async function uploadEncryptedFile(page: Page, filePath: string) {
-  await page.getByTestId("files-button").click();
-  // No modal flow - `files-button` triggers the native picker directly.
+  // Drive the hidden input directly to avoid native file-picker side effects.
   await page.locator('[data-testid="file-input"]').setInputFiles(filePath);
 }
 
@@ -153,8 +152,6 @@ test.describe("Encrypted PDF Unlock Modal", () => {
   }) => {
     await mockRemovePasswordSuccess(page);
 
-    await page.getByTestId("files-button").click();
-    // No modal flow - `files-button` triggers the native picker directly.
     await page.locator('[data-testid="file-input"]').setInputFiles([
       {
         name: "encrypted-a.pdf",
diff --git a/frontend/editor/src/core/tests/stubbed/files-page-screenshots.spec.ts b/frontend/editor/src/core/tests/stubbed/files-page-screenshots.spec.ts
index da4d889a9d..2256f9ab50 100644
--- a/frontend/editor/src/core/tests/stubbed/files-page-screenshots.spec.ts
+++ b/frontend/editor/src/core/tests/stubbed/files-page-screenshots.spec.ts
@@ -13,6 +13,7 @@ interface SeedFile {
 }
 
 async function seedFiles(page: Page, files: SeedFile[]): Promise<void> {
+  const seedKey = "stirling-pdf-files-page-seeded";
   // Build the server-side view from the cloud entries so reconcileServerFiles
   // sees them as still-existing on the server (otherwise they get detached
   // and the cloud cards vanish before the screenshot is taken).
@@ -36,7 +37,10 @@ async function seedFiles(page: Page, files: SeedFile[]): Promise<void> {
     route.fulfill({ json: serverFiles }),
   );
   await page.addInitScript(
-    ({ records, dbVersion }) => {
+    ({ records, dbVersion, seedKey }) => {
+      if (window.localStorage.getItem(seedKey) === "1") {
+        return;
+      }
       const open = window.indexedDB.open("stirling-pdf-files", dbVersion);
       open.onupgradeneeded = (event) => {
         const db = (event.target as IDBOpenDBRequest).result;
@@ -93,10 +97,20 @@ async function seedFiles(page: Page, files: SeedFile[]): Promise<void> {
             remoteShareToken: null,
           });
         }
-        tx.oncomplete = () => db.close();
+        tx.oncomplete = () => {
+          db.close();
+          window.localStorage.setItem(seedKey, "1");
+          if (location.pathname.startsWith("/files")) {
+            location.reload();
+          }
+        };
       };
     },
-    { records: files, dbVersion: DATABASE_CONFIGS.FILES.version },
+    {
+      records: files,
+      dbVersion: DATABASE_CONFIGS.FILES.version,
+      seedKey,
+    },
   );
 }
 
@@ -462,6 +476,7 @@ test.describe("Files page screenshots", () => {
       { id: "bravo", name: "bravo.pdf", remoteStorageId: null },
     ]);
     await page.goto("/files", { waitUntil: "domcontentloaded" });
+    await page.waitForLoadState("domcontentloaded");
     await expect(
       page.locator(".files-page-card:not(.files-page-skeleton-card)").first(),
     ).toBeVisible({
@@ -478,6 +493,7 @@ test.describe("Files page screenshots", () => {
       { id: "alpha", name: "alpha.pdf", remoteStorageId: null },
     ]);
     await page.goto("/files", { waitUntil: "domcontentloaded" });
+    await page.waitForLoadState("domcontentloaded");
     await expect(
       page.locator(".files-page-card:not(.files-page-skeleton-card)").first(),
     ).toBeVisible({
@@ -506,6 +522,7 @@ test.describe("Files page screenshots", () => {
       { id: "alpha", name: "alpha.pdf", remoteStorageId: null },
     ]);
     await page.goto("/files", { waitUntil: "domcontentloaded" });
+    await page.waitForLoadState("domcontentloaded");
     await expect(
       page.locator(".files-page-card:not(.files-page-skeleton-card)").first(),
     ).toBeVisible({
diff --git a/frontend/editor/src/core/tests/stubbed/files-page.spec.ts b/frontend/editor/src/core/tests/stubbed/files-page.spec.ts
index 081d1c83f1..ec1af4dc8d 100644
--- a/frontend/editor/src/core/tests/stubbed/files-page.spec.ts
+++ b/frontend/editor/src/core/tests/stubbed/files-page.spec.ts
@@ -14,6 +14,7 @@ interface SeedFile {
 
 /** Seed IDB + register the cloud entries with the server stub. */
 async function seedFiles(page: Page, files: SeedFile[]): Promise<void> {
+  const seedKey = "stirling-pdf-files-page-seeded";
   // Build the server-side view from the cloud entries so reconcileServerFiles
   // sees them as still-existing on the server (otherwise they get detached).
   const serverFiles = files
@@ -36,7 +37,10 @@ async function seedFiles(page: Page, files: SeedFile[]): Promise<void> {
     route.fulfill({ json: serverFiles }),
   );
   await page.addInitScript(
-    ({ records, dbVersion }) => {
+    ({ records, dbVersion, seedKey }) => {
+      if (window.localStorage.getItem(seedKey) === "1") {
+        return;
+      }
       const open = window.indexedDB.open("stirling-pdf-files", dbVersion);
       open.onupgradeneeded = (event) => {
         const db = (event.target as IDBOpenDBRequest).result;
@@ -94,10 +98,20 @@ async function seedFiles(page: Page, files: SeedFile[]): Promise<void> {
             remoteShareToken: null,
           });
         }
-        tx.oncomplete = () => db.close();
+        tx.oncomplete = () => {
+          db.close();
+          window.localStorage.setItem(seedKey, "1");
+          if (location.pathname.startsWith("/files")) {
+            location.reload();
+          }
+        };
       };
     },
-    { records: files, dbVersion: DATABASE_CONFIGS.FILES.version },
+    {
+      records: files,
+      dbVersion: DATABASE_CONFIGS.FILES.version,
+      seedKey,
+    },
   );
 }
 
@@ -823,10 +837,8 @@ test.describe("Files page", () => {
       await page.locator("#filesPage-tab-sharedByMe").click();
       const sharedByMeCards = page.locator(".files-page-card:not(.is-folder)");
       await expect(sharedByMeCards).toHaveCount(2, { timeout: 3_000 });
-      await expect(sharedByMeCards).toContainText([
-        "link-shared.pdf",
-        "user-shared.pdf",
-      ]);
+      await expect(sharedByMeCards.filter({ hasText: "link-shared.pdf" })).toHaveCount(1);
+      await expect(sharedByMeCards.filter({ hasText: "user-shared.pdf" })).toHaveCount(1);
 
       // "Shared with me" -> only from-someone-else.pdf
       await page.locator("#filesPage-tab-shared").click();
diff --git a/frontend/editor/src/core/tests/stubbed/pdf-text-search.spec.ts b/frontend/editor/src/core/tests/stubbed/pdf-text-search.spec.ts
index 5ba1599386..56ff90e4b2 100644
--- a/frontend/editor/src/core/tests/stubbed/pdf-text-search.spec.ts
+++ b/frontend/editor/src/core/tests/stubbed/pdf-text-search.spec.ts
@@ -16,9 +16,8 @@ test.describe("Reader - in-document text search", () => {
     await page.goto("/read");
     await page.waitForLoadState("domcontentloaded");
 
-    // Upload a PDF first so the reader has content. `files-button` now
-    // triggers the native picker directly - no modal flow involved.
-    await page.getByTestId("files-button").click();
+    // Upload a PDF first so the reader has content. Drive the hidden input
+    // directly to avoid Firefox file-picker side effects.
     await page.locator('[data-testid="file-input"]').setInputFiles(SAMPLE_PDF);
 
     // The WorkbenchBar exposes a "Search PDF" button (aria-label="Search PDF")