fixes #75703

src/vs/base/browser/ui/menu/menubar.ts

@@ -18,6 +18,7 @@ import { KeyCode, ResolvedKeybinding } from 'vs/base/common/keyCodes';
 import { Disposable, dispose, IDisposable, DisposableStore } from 'vs/base/common/lifecycle';
 import { withNullAsUndefined } from 'vs/base/common/types';
 import { asArray } from 'vs/base/common/arrays';
+import { ScanCodeUtils, ScanCode } from 'vs/base/common/scanCode';
 
 const $ = DOM.$;
 
@@ -777,6 +778,13 @@ export class MenuBar extends Disposable {
 			return;
 		}
 
+		// Prevent alt-key default if the menu is not hidden and we use alt to focus
+		if (modifierKeyStatus.event && !this.options.disableAltFocus) {
+			if (ScanCodeUtils.toEnum(modifierKeyStatus.event.code) === ScanCode.AltLeft) {
+				modifierKeyStatus.event.preventDefault();
+			}
+		}
+
 		// Alt key pressed while menu is focused. This should return focus away from the menubar
 		if (this.isFocused && modifierKeyStatus.lastKeyPressed === 'alt' && modifierKeyStatus.altKey) {
 			this.setUnfocusedState();
@@ -892,6 +900,7 @@ interface IModifierKeyStatus {
 	ctrlKey: boolean;
 	lastKeyPressed?: ModifierKey;
 	lastKeyReleased?: ModifierKey;
+	event?: KeyboardEvent;
 }
 
 
@@ -930,6 +939,7 @@ class ModifierKeyEmitter extends Emitter<IModifierKeyStatus> {
 			this._keyStatus.shiftKey = e.shiftKey;
 
 			if (this._keyStatus.lastKeyPressed) {
+				this._keyStatus.event = e;
 				this.fire(this._keyStatus);
 			}
 		}));
@@ -954,6 +964,7 @@ class ModifierKeyEmitter extends Emitter<IModifierKeyStatus> {
 			this._keyStatus.shiftKey = e.shiftKey;
 
 			if (this._keyStatus.lastKeyReleased) {
+				this._keyStatus.event = e;
 				this.fire(this._keyStatus);
 			}
 		}));

src/vs/workbench/browser/main.contribution.ts

+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import * as nls from 'vs/nls';
+import { Registry } from 'vs/platform/registry/common/platform';
+import { IConfigurationRegistry, Extensions as ConfigurationExtensions, ConfigurationScope } from 'vs/platform/configuration/common/configurationRegistry';
+import { isWindows, isLinux } from 'vs/base/common/platform';
+
+
+// Configuration
+(function registerConfiguration(): void {
+	const registry = Registry.as<IConfigurationRegistry>(ConfigurationExtensions.Configuration);
+
+	// Window
+	registry.registerConfiguration({
+		'id': 'window',
+		'order': 8,
+		'title': nls.localize('windowConfigurationTitle', "Window"),
+		'type': 'object',
+		'properties': {
+			'window.menuBarVisibility': {
+				'type': 'string',
+				'enum': ['default', 'visible', 'toggle', 'hidden'],
+				'enumDescriptions': [
+					nls.localize('window.menuBarVisibility.default', "Menu is only hidden in full screen mode."),
+					nls.localize('window.menuBarVisibility.visible', "Menu is always visible even in full screen mode."),
+					nls.localize('window.menuBarVisibility.toggle', "Menu is hidden but can be displayed via Alt key."),
+					nls.localize('window.menuBarVisibility.hidden', "Menu is always hidden.")
+				],
+				'default': 'default',
+				'scope': ConfigurationScope.APPLICATION,
+				'description': nls.localize('menuBarVisibility', "Control the visibility of the menu bar. A setting of 'toggle' means that the menu bar is hidden and a single press of the Alt key will show it. By default, the menu bar will be visible, unless the window is full screen."),
+				'included': isWindows || isLinux
+			},
+			'window.enableMenuBarMnemonics': {
+				'type': 'boolean',
+				'default': true,
+				'scope': ConfigurationScope.APPLICATION,
+				'description': nls.localize('enableMenuBarMnemonics', "If enabled, the main menus can be opened via Alt-key shortcuts. Disabling mnemonics allows to bind these Alt-key shortcuts to editor commands instead."),
+				'included': isWindows || isLinux
+			},
+			'window.disableCustomMenuBarAltFocus': {
+				'type': 'boolean',
+				'default': false,
+				'scope': ConfigurationScope.APPLICATION,
+				'markdownDescription': nls.localize('disableCustomMenuBarAltFocus', "If enabled, disables the ability to focus the menu bar with the Alt-key when not set to toggle."),
+				'included': isWindows || isLinux
+			}
+		}
+	});
+})();
\ No newline at end of file

src/vs/workbench/browser/parts/titlebar/menubarControl.ts

@@ -34,6 +34,8 @@ import { assign } from 'vs/base/common/objects';
 import { mnemonicMenuLabel, unmnemonicLabel } from 'vs/base/common/labels';
 import { IAccessibilityService, AccessibilitySupport } from 'vs/platform/accessibility/common/accessibility';
 import { withNullAsUndefined } from 'vs/base/common/types';
+import { IWorkbenchLayoutService } from 'vs/workbench/services/layout/browser/layoutService';
+import { isFullscreen } from 'vs/base/browser/browser';
 
 export abstract class MenubarControl extends Disposable {
 
@@ -106,8 +108,6 @@ export abstract class MenubarControl extends Disposable {
 		this.menuUpdater = this._register(new RunOnceScheduler(() => this.doUpdateMenubar(false), 200));
 
 		this.notifyUserOfCustomMenubarAccessibility();
-
-		this.registerListeners();
 	}
 
 	protected abstract doUpdateMenubar(firstTime: boolean): void;
@@ -300,6 +300,8 @@ export class NativeMenubarControl extends MenubarControl {
 
 			this.doUpdateMenubar(true);
 		});
+
+		this.registerListeners();
 	}
 
 	protected doUpdateMenubar(firstTime: boolean): void {
@@ -457,7 +459,8 @@ export class CustomMenubarControl extends MenubarControl {
 		@IPreferencesService preferencesService: IPreferencesService,
 		@IEnvironmentService environmentService: IEnvironmentService,
 		@IAccessibilityService accessibilityService: IAccessibilityService,
-		@IThemeService private readonly themeService: IThemeService
+		@IThemeService private readonly themeService: IThemeService,
+		@IWorkbenchLayoutService private readonly layoutService: IWorkbenchLayoutService
 	) {
 
 		super(
@@ -482,6 +485,8 @@ export class CustomMenubarControl extends MenubarControl {
 			this.recentlyOpened = recentlyOpened;
 		});
 
+		this.registerListeners();
+
 		registerThemingParticipant((theme: ITheme, collector: ICssStyleCollector) => {
 			const menubarActiveWindowFgColor = theme.getColor(TITLE_BAR_ACTIVE_FOREGROUND);
 			if (menubarActiveWindowFgColor) {
@@ -642,7 +647,7 @@ export class CustomMenubarControl extends MenubarControl {
 			enableMenuBarMnemonics = true;
 		}
 
-		return enableMenuBarMnemonics;
+		return enableMenuBarMnemonics && (!isWeb || isFullscreen());
 	}
 
 	private setupCustomMenubar(firstTime: boolean): void {
@@ -750,6 +755,11 @@ export class CustomMenubarControl extends MenubarControl {
 		this._register(DOM.addDisposableListener(window, DOM.EventType.RESIZE, () => {
 			this.menubar.blur();
 		}));
+
+		// Mnemonics require fullscreen in web
+		if (isWeb) {
+			this._register(this.layoutService.onFullscreenChange(e => this.updateMenubar()));
+		}
 	}
 
 	get onVisibilityChange(): Event<boolean> {

src/vs/workbench/workbench.web.main.ts

@@ -9,7 +9,7 @@ import 'vs/editor/editor.all';
 
 import 'vs/workbench/api/browser/extensionHost.contribution';
 
-// import 'vs/workbench/electron-browser/main.contribution';
+import 'vs/workbench/browser/main.contribution';
 import 'vs/workbench/browser/workbench.contribution';
 
 import 'vs/workbench/browser/web.main';