diff --git chrome/browser/ui/javascript_dialogs/javascript_tab_modal_dialog_manager_delegate_desktop.cc chrome/browser/ui/javascript_dialogs/javascript_tab_modal_dialog_manager_delegate_desktop.cc
index 8b3ce4e53ef25..7fcec86f074e3 100644
--- chrome/browser/ui/javascript_dialogs/javascript_tab_modal_dialog_manager_delegate_desktop.cc
+++ chrome/browser/ui/javascript_dialogs/javascript_tab_modal_dialog_manager_delegate_desktop.cc
@@ -6,6 +6,7 @@
 
 #include <utility>
 
+#include "cef/libcef/features/features.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/browser/ui/browser_finder.h"
 #include "chrome/browser/ui/browser_list.h"
@@ -28,6 +29,22 @@
 #include "chrome/browser/safe_browsing/user_interaction_observer.h"
 #endif
 
+#if BUILDFLAG(ENABLE_CEF)
+#include "cef/libcef/browser/chrome/extensions/chrome_extension_util.h"
+#endif
+
+namespace {
+
+bool IsAlloyContents(content::WebContents* web_contents) {
+#if BUILDFLAG(ENABLE_CEF)
+  return cef::IsAlloyContents(web_contents, /*primary_only=*/true);
+#else
+  return false;
+#endif
+}
+
+}  // namespace
+
 JavaScriptTabModalDialogManagerDelegateDesktop::
     JavaScriptTabModalDialogManagerDelegateDesktop(
         content::WebContents* web_contents)
@@ -77,6 +94,9 @@ void JavaScriptTabModalDialogManagerDelegateDesktop::SetTabNeedsAttention(
 bool JavaScriptTabModalDialogManagerDelegateDesktop::IsWebContentsForemost() {
   Browser* browser = BrowserList::GetInstance()->GetLastActive();
   if (!browser) {
+    if (IsAlloyContents(web_contents_)) {
+      return true;
+    }
     // It's rare, but there are crashes from where sites are trying to show
     // dialogs in the split second of time between when their Browser is gone
     // and they're gone. In that case, bail. https://crbug.com/1142806
@@ -92,7 +112,11 @@ bool JavaScriptTabModalDialogManagerDelegateDesktop::IsApp() {
 }
 
 bool JavaScriptTabModalDialogManagerDelegateDesktop::CanShowModalUI() {
-  tabs::TabInterface* tab = tabs::TabInterface::GetFromContents(web_contents_);
+  tabs::TabInterface* tab =
+      tabs::TabInterface::MaybeGetFromContents(web_contents_);
+  if (!tab && IsAlloyContents(web_contents_)) {
+    return true;
+  }
   return tab && tab->CanShowModalUI();
 }
 
diff --git chrome/browser/ui/views/javascript_tab_modal_dialog_view_views.cc chrome/browser/ui/views/javascript_tab_modal_dialog_view_views.cc
index 3c56e658d05c4..980caca1469bd 100644
--- chrome/browser/ui/views/javascript_tab_modal_dialog_view_views.cc
+++ chrome/browser/ui/views/javascript_tab_modal_dialog_view_views.cc
@@ -79,10 +79,13 @@ JavaScriptTabModalDialogViewViews::JavaScriptTabModalDialogViewViews(
       default_prompt_text_(default_prompt_text),
       dialog_callback_(std::move(dialog_callback)),
       dialog_force_closed_callback_(std::move(dialog_force_closed_callback)) {
+  // Will be nullptr with CEF Alloy style browsers.
   tabs::TabInterface* tab =
-      tabs::TabInterface::GetFromContents(parent_web_contents);
-  CHECK(tab && tab->CanShowModalUI());
-  scoped_tab_modal_ui_ = tab->ShowModalUI();
+      tabs::TabInterface::MaybeGetFromContents(parent_web_contents);
+  if (tab) {
+    CHECK(tab->CanShowModalUI());
+    scoped_tab_modal_ui_ = tab->ShowModalUI();
+  }
 
   SetModalType(ui::mojom::ModalType::kChild);
   SetDefaultButton(static_cast<int>(ui::mojom::DialogButton::kOk));