diff --git a/packages/playwright-core/src/server/chromium/chromium.ts b/packages/playwright-core/src/server/chromium/chromium.ts
index e745cca214..5161c32a97 100644
--- a/packages/playwright-core/src/server/chromium/chromium.ts
+++ b/packages/playwright-core/src/server/chromium/chromium.ts
@@ -131,7 +131,7 @@ export class Chromium extends BrowserType {
     return directory ? new CRDevTools(path.join(directory, 'devtools-preferences.json')) : undefined;
   }
 
-  async _connectToTransport(transport: ConnectionTransport, options: BrowserOptions): Promise<CRBrowser> {
+  override async _connectToTransport(transport: ConnectionTransport, options: BrowserOptions): Promise<CRBrowser> {
     let devtools = this._devtools;
     if ((options as any).__testHookForDevTools) {
       devtools = this._createDevTools();
@@ -140,7 +140,7 @@ export class Chromium extends BrowserType {
     return CRBrowser.connect(this.attribution.playwright, transport, options, devtools);
   }
 
-  _doRewriteStartupLog(error: ProtocolError): ProtocolError {
+  override _doRewriteStartupLog(error: ProtocolError): ProtocolError {
     if (!error.logs)
       return error;
     if (error.logs.includes('Missing X server'))
@@ -161,11 +161,11 @@ export class Chromium extends BrowserType {
     return error;
   }
 
-  _amendEnvironment(env: Env, userDataDir: string, executable: string, browserArguments: string[]): Env {
+  override _amendEnvironment(env: Env, userDataDir: string, executable: string, browserArguments: string[]): Env {
     return env;
   }
 
-  _attemptToGracefullyCloseBrowser(transport: ConnectionTransport): void {
+  override _attemptToGracefullyCloseBrowser(transport: ConnectionTransport): void {
     const message: ProtocolRequest = { method: 'Browser.close', id: kBrowserCloseMessageId, params: {} };
     transport.send(message);
   }
@@ -277,7 +277,7 @@ export class Chromium extends BrowserType {
     }
   }
 
-  _defaultArgs(options: types.LaunchOptions, isPersistent: boolean, userDataDir: string): string[] {
+  override _defaultArgs(options: types.LaunchOptions, isPersistent: boolean, userDataDir: string): string[] {
     const chromeArguments = this._innerDefaultArgs(options);
     chromeArguments.push(`--user-data-dir=${userDataDir}`);
     if (options.useWebSocket)
diff --git a/packages/playwright-core/src/server/firefox/firefox.ts b/packages/playwright-core/src/server/firefox/firefox.ts
index 96d1edae4c..4958e58f42 100644
--- a/packages/playwright-core/src/server/firefox/firefox.ts
+++ b/packages/playwright-core/src/server/firefox/firefox.ts
@@ -33,11 +33,11 @@ export class Firefox extends BrowserType {
     super(parent, 'firefox');
   }
 
-  _connectToTransport(transport: ConnectionTransport, options: BrowserOptions): Promise<FFBrowser> {
+  override _connectToTransport(transport: ConnectionTransport, options: BrowserOptions): Promise<FFBrowser> {
     return FFBrowser.connect(this.attribution.playwright, transport, options);
   }
 
-  _doRewriteStartupLog(error: ProtocolError): ProtocolError {
+  override _doRewriteStartupLog(error: ProtocolError): ProtocolError {
     if (!error.logs)
       return error;
     // https://github.com/microsoft/playwright/issues/6500
@@ -48,7 +48,7 @@ export class Firefox extends BrowserType {
     return error;
   }
 
-  _amendEnvironment(env: Env, userDataDir: string, executable: string, browserArguments: string[]): Env {
+  override _amendEnvironment(env: Env, userDataDir: string, executable: string, browserArguments: string[]): Env {
     if (!path.isAbsolute(os.homedir()))
       throw new Error(`Cannot launch Firefox with relative home directory. Did you set ${os.platform() === 'win32' ? 'USERPROFILE' : 'HOME'} to a relative path?`);
     if (os.platform() === 'linux') {
@@ -60,12 +60,12 @@ export class Firefox extends BrowserType {
     return env;
   }
 
-  _attemptToGracefullyCloseBrowser(transport: ConnectionTransport): void {
+  override _attemptToGracefullyCloseBrowser(transport: ConnectionTransport): void {
     const message = { method: 'Browser.close', params: {}, id: kBrowserCloseMessageId };
     transport.send(message);
   }
 
-  _defaultArgs(options: types.LaunchOptions, isPersistent: boolean, userDataDir: string): string[] {
+  override _defaultArgs(options: types.LaunchOptions, isPersistent: boolean, userDataDir: string): string[] {
     const { args = [], headless } = options;
     const userDataDirArg = args.find(arg => arg.startsWith('-profile') || arg.startsWith('--profile'));
     if (userDataDirArg)
diff --git a/packages/playwright-core/src/server/playwright.ts b/packages/playwright-core/src/server/playwright.ts
index c4ffd518ce..3d524ad959 100644
--- a/packages/playwright-core/src/server/playwright.ts
+++ b/packages/playwright-core/src/server/playwright.ts
@@ -28,6 +28,7 @@ import { debugLogger } from '../utils/debugLogger';
 import type { Page } from './page';
 import { DebugController } from './debugController';
 import type { Language } from '../utils/isomorphic/locatorGenerators';
+import type { BrowserType } from './browserType';
 
 type PlaywrightOptions = {
   socksProxyPort?: number;
@@ -38,11 +39,11 @@ type PlaywrightOptions = {
 
 export class Playwright extends SdkObject {
   readonly selectors: Selectors;
-  readonly chromium: Chromium;
+  readonly chromium: BrowserType;
   readonly android: Android;
   readonly electron: Electron;
-  readonly firefox: Firefox;
-  readonly webkit: WebKit;
+  readonly firefox: BrowserType;
+  readonly webkit: BrowserType;
   readonly options: PlaywrightOptions;
   readonly debugController: DebugController;
   private _allPages = new Set<Page>();
diff --git a/packages/playwright-core/src/server/webkit/webkit.ts b/packages/playwright-core/src/server/webkit/webkit.ts
index 33f4a68c20..778b5601a0 100644
--- a/packages/playwright-core/src/server/webkit/webkit.ts
+++ b/packages/playwright-core/src/server/webkit/webkit.ts
@@ -32,15 +32,15 @@ export class WebKit extends BrowserType {
     super(parent, 'webkit');
   }
 
-  _connectToTransport(transport: ConnectionTransport, options: BrowserOptions): Promise<WKBrowser> {
+  override _connectToTransport(transport: ConnectionTransport, options: BrowserOptions): Promise<WKBrowser> {
     return WKBrowser.connect(this.attribution.playwright, transport, options);
   }
 
-  _amendEnvironment(env: Env, userDataDir: string, executable: string, browserArguments: string[]): Env {
+  override _amendEnvironment(env: Env, userDataDir: string, executable: string, browserArguments: string[]): Env {
     return { ...env, CURL_COOKIE_JAR_PATH: path.join(userDataDir, 'cookiejar.db') };
   }
 
-  _doRewriteStartupLog(error: ProtocolError): ProtocolError {
+  override _doRewriteStartupLog(error: ProtocolError): ProtocolError {
     if (!error.logs)
       return error;
     if (error.logs.includes('cannot open display'))
@@ -48,11 +48,11 @@ export class WebKit extends BrowserType {
     return error;
   }
 
-  _attemptToGracefullyCloseBrowser(transport: ConnectionTransport): void {
+  override _attemptToGracefullyCloseBrowser(transport: ConnectionTransport): void {
     transport.send({ method: 'Playwright.close', params: {}, id: kBrowserCloseMessageId });
   }
 
-  _defaultArgs(options: types.LaunchOptions, isPersistent: boolean, userDataDir: string): string[] {
+  override _defaultArgs(options: types.LaunchOptions, isPersistent: boolean, userDataDir: string): string[] {
     const { args = [], proxy, headless } = options;
     const userDataDirArg = args.find(arg => arg.startsWith('--user-data-dir'));
     if (userDataDirArg)