diff --git a/main.js b/main.js
index cc35d6f..cd0f3e2 100644
--- a/main.js
+++ b/main.js
@@ -139,13 +139,19 @@ function createWindow(startUrl) {
   const win = new BrowserWindow(windowOptions);
   perfMarks.browserWindow_instantiated = performance.now();
 
-  // Allow window.open() popups (e.g. OAuth / SSO / school portals) so that
-  // POST form submissions and opener relationships are preserved.
-  // We still restrict to http/https for safety; everything else is denied.
-  win.webContents.setWindowOpenHandler(({ url }) => {
-    if (url.startsWith('http://') || url.startsWith('https://')) {
-      return { action: 'allow' };
+  // Intercept window.open() requests and route them into the existing window as a new tab
+  // instead of spawning separate BrowserWindows. We still allow a small OAuth allowlist
+  // (accounts.google.com, login.microsoftonline.com, oauth, sso) to open real popups if
+  // the flow depends on window.opener relationships. Everything else becomes a new tab.
+  win.webContents.setWindowOpenHandler((details) => {
+    const { url } = details;
+    if (!/^https?:\/\//i.test(url)) return { action: 'deny' };
+    // OAuth / SSO allowlist heuristic
+    if (/accounts\.google\.com|microsoftonline\.com|oauth|login|signin|sso/i.test(url)) {
+      return { action: 'allow' }; // preserve popup semantics for complex auth flows
     }
+    // Forward to renderer to open as tab
+    try { win.webContents.send('open-url-new-tab', url); } catch {}
     return { action: 'deny' };
   });
 
@@ -161,11 +167,18 @@ function createWindow(startUrl) {
 
   // ensure all embedded <webview> tags behave predictably without heavy injections
   win.webContents.on('did-attach-webview', (event, webContents) => {
-    // Allow popups inside <webview> as well (required for some login flows)
-    webContents.setWindowOpenHandler(({ url }) => {
-      if (url.startsWith('http://') || url.startsWith('https://')) {
-        return { action: 'allow' };
+    // Route <webview> window.open() calls to tabs unless OAuth allowlist matched
+    webContents.setWindowOpenHandler((details) => {
+      const { url } = details;
+      if (!/^https?:\/\//i.test(url)) return { action: 'deny' };
+      if (/accounts\.google\.com|microsoftonline\.com|oauth|login|signin|sso/i.test(url)) {
+        return { action: 'allow' }; // keep popup for auth
       }
+      // Send to the owning window (embedder) to open a new tab
+      try {
+        const host = webContents.hostWebContents || webContents;
+        host.send('open-url-new-tab', url);
+      } catch {}
       return { action: 'deny' };
     });
   });
diff --git a/renderer/script.js b/renderer/script.js
index 9023e4a..1a6198b 100644
--- a/renderer/script.js
+++ b/renderer/script.js
@@ -182,9 +182,17 @@ loadBookmarks();
 // Remove iframe-based navigation listener (using webview IPC now)
 
 // Listen for site history updates from main process
-ipcRenderer.on('record-site-history', (event, url) => {
+// NOTE: electronAPI.on wrapper strips the original event object and only forwards args.
+// Handlers therefore must NOT expect the event parameter.
+ipcRenderer.on('record-site-history', (url) => {
   debug('[DEBUG] Received site history update:', url);
-  addToSiteHistory(url);
+  if (typeof url === 'string' && url) addToSiteHistory(url);
+});
+
+// Main process requests opening a URL in a new tab (window.open interception)
+ipcRenderer.on('open-url-new-tab', (url) => {
+  console.log('[DEBUG] IPC open-url-new-tab received:', url);
+  if (typeof url === 'string' && url) createTab(url);
 });
 
 // Auto-open on download start is disabled by design now.
@@ -290,19 +298,22 @@ function createTab(inputUrl) {
   webview.addEventListener('did-finish-load', () => {
     scheduleUpdateNavButtons();
   });
+  // Catch failed loads for diagnostics (e.g., http -> https transitions failing)
+  webview.addEventListener('did-fail-load', (e) => {
+    console.warn('[DEBUG] did-fail-load (createTab) id:', id, 'code:', e.errorCode, 'desc:', e.errorDescription, 'validatedURL:', e.validatedURL, 'isMainFrame:', e.isMainFrame);
+  });
 
   // catch any target="_blank" or window.open() calls and open them as new tabs
   webview.addEventListener('new-window', e => {
-    // Allow auth / SSO popup windows (don't preventDefault) when target is http(s)
-    // so form POST + redirect chains stay intact. For simple links attempting to
-    // open a new tab, we create an in-app tab instead. Heuristic: if disposition
-    // is 'foreground-tab' or 'background-tab', treat as tab; otherwise allow popup.
-    if (e.url && (e.url.startsWith('http://') || e.url.startsWith('https://'))) {
-      if (e.disposition && e.disposition.includes('tab')) {
-        e.preventDefault();
-        createTab(e.url);
-      } // else let Electron create a real popup window
+    // Always open external http(s) targets in a new in-app tab instead of spawning
+    // a separate Electron BrowserWindow. (User request)
+    // If you need to allow real popup windows for specific OAuth flows later,
+    // introduce an allowlist check here before preventDefault().
+    if (e.url && /^https?:\/\//i.test(e.url)) {
+      e.preventDefault();
+      createTab(e.url);
     } else {
+      // Block other scheme popups for safety (could extend with custom handling)
       e.preventDefault();
     }
   });
@@ -563,12 +574,10 @@ function convertHomeTabToWebview(tabId, inputUrl, resolvedUrl) {
   });
 
   webview.addEventListener('new-window', e => {
-    if (e.url && (e.url.startsWith('http://') || e.url.startsWith('https://'))) {
-      if (e.disposition && e.disposition.includes('tab')) {
-        e.preventDefault();
-        createTab(e.url);
-      }
-      // otherwise allow popup for auth
+    // Unified behavior: always open http(s) targets in a new tab (no extra window)
+    if (e.url && /^https?:\/\//i.test(e.url)) {
+      e.preventDefault();
+      createTab(e.url);
     } else {
       e.preventDefault();
     }
@@ -926,12 +935,12 @@ function renderTabs() {
 }
 
 // 1) handle URL sent by main for a detached window
-ipcRenderer.on('open-url', (event, url) => {
+ipcRenderer.on('open-url', (url) => {
   tabs = [];
   activeTabId = null;
   webviewsEl.innerHTML = '';
   tabBarEl.innerHTML = '';
-  createTab(url);
+  if (typeof url === 'string' && url) createTab(url); else createTab();
 });
 
 function goBack() {