diff --git a/docs/api.md b/docs/api.md
index bb4446a21e1c02..8263c59b2f2481 100644
--- a/docs/api.md
+++ b/docs/api.md
@@ -3688,6 +3688,7 @@ const browser = await chromium.launch({  // Or 'firefox' or 'webkit'.
   - `dumpio` <[boolean]> Whether to pipe the browser process stdout and stderr into `process.stdout` and `process.stderr`. Defaults to `false`.
   - `env` <[Object]> Specify environment variables that will be visible to the browser. Defaults to `process.env`.
   - `devtools` <[boolean]> **Chromium-only** Whether to auto-open a Developer Tools panel for each tab. If this option is `true`, the `headless` option will be set `false`.
+  - `slowMo` <[number]> Slows down Playwright operations by the specified amount of milliseconds. Useful so that you can see what is going on. Defaults to 0.
 - returns: <[Promise]<[BrowserContext]>> Promise which resolves to the browser app instance.
 
 Launches browser instance that uses persistent storage located at `userDataDir`.
diff --git a/src/browser.ts b/src/browser.ts
index 4caabc079da8f7..02cb42c305c074 100644
--- a/src/browser.ts
+++ b/src/browser.ts
@@ -27,11 +27,6 @@ export interface Browser extends platform.EventEmitterType {
   _setDebugFunction(debugFunction: (message: string) => void): void;
 }
 
-export type ConnectOptions = {
-  slowMo?: number,
-  wsEndpoint: string
-};
-
 export async function createPageInNewContext(browser: Browser, options?: BrowserContextOptions): Promise<Page> {
   const context = await browser.newContext(options);
   const page = await context.newPage();
diff --git a/src/server/browserType.ts b/src/server/browserType.ts
index 7b76cf4dcc546c..5dc7e7d0eb56d0 100644
--- a/src/server/browserType.ts
+++ b/src/server/browserType.ts
@@ -14,7 +14,6 @@
  * limitations under the License.
  */
 
-import { ConnectOptions } from '../browser';
 import { BrowserContext } from '../browserContext';
 import { BrowserServer } from './browserServer';
 
@@ -24,7 +23,7 @@ export type BrowserArgOptions = {
   devtools?: boolean,
 };
 
-export type LaunchOptions = BrowserArgOptions & {
+export type ProcessOptions = BrowserArgOptions & {
   executablePath?: string,
   ignoreDefaultArgs?: boolean | string[],
   handleSIGINT?: boolean,
@@ -39,11 +38,21 @@ export type LaunchOptions = BrowserArgOptions & {
   env?: {[key: string]: string} | undefined
 };
 
+export type ConnectOptions = {
+  wsEndpoint: string
+} & BrowserOptions;
+
+type BrowserOptions = {
+  slowMo?: number,
+}
+
+export type LaunchOptions = ProcessOptions & BrowserOptions;
+export type ServerOptions = ProcessOptions & { port?: number };
 export interface BrowserType<Browser> {
   executablePath(): string;
   name(): string;
-  launch(options?: LaunchOptions & { slowMo?: number }): Promise<Browser>;
-  launchServer(options?: LaunchOptions & { port?: number }): Promise<BrowserServer>;
+  launch(options?: LaunchOptions): Promise<Browser>;
+  launchServer(options?: ServerOptions): Promise<BrowserServer>;
   launchPersistentContext(userDataDir: string, options?: LaunchOptions): Promise<BrowserContext>;
   connect(options: ConnectOptions): Promise<Browser>;
 }
diff --git a/src/server/chromium.ts b/src/server/chromium.ts
index 0751ca698a2ee3..f5617e2c0c0a79 100644
--- a/src/server/chromium.ts
+++ b/src/server/chromium.ts
@@ -18,15 +18,15 @@
 import * as fs from 'fs';
 import * as os from 'os';
 import * as path from 'path';
-import { debugError, helper } from '../helper';
+import { debugError, helper, assert } from '../helper';
 import { CRBrowser } from '../chromium/crBrowser';
 import * as platform from '../platform';
 import * as ws from 'ws';
 import { launchProcess } from '../server/processLauncher';
 import { kBrowserCloseMessageId } from '../chromium/crConnection';
 import { PipeTransport } from './pipeTransport';
-import { LaunchOptions, BrowserArgOptions, BrowserType } from './browserType';
-import { ConnectOptions, LaunchType } from '../browser';
+import { LaunchOptions, BrowserArgOptions, BrowserType, ProcessOptions, ConnectOptions, ServerOptions } from './browserType';
+import { LaunchType } from '../browser';
 import { BrowserServer, WebSocketWrapper } from './browserServer';
 import { Events } from '../events';
 import { ConnectionTransport, ProtocolRequest } from '../transport';
@@ -45,28 +45,30 @@ export class Chromium implements BrowserType<CRBrowser> {
     return 'chromium';
   }
 
-  async launch(options?: LaunchOptions & { slowMo?: number }): Promise<CRBrowser> {
-    if (options && (options as any).userDataDir)
-      throw new Error('userDataDir option is not supported in `browserType.launch`. Use `browserType.launchPersistentContext` instead');
+  async launch(options: LaunchOptions = {}): Promise<CRBrowser> {
+    assert(!(options as any).userDataDir, 'userDataDir option is not supported in `browserType.launch`. Use `browserType.launchPersistentContext` instead');
     const { browserServer, transport } = await this._launchServer(options, 'local');
-    const browser = await CRBrowser.connect(transport!, false, options && options.slowMo);
+    const browser = await CRBrowser.connect(transport!, false, options.slowMo);
     (browser as any)['__server__'] = browserServer;
     return browser;
   }
 
-  async launchServer(options?: LaunchOptions & { port?: number }): Promise<BrowserServer> {
-    return (await this._launchServer(options, 'server', undefined, options && options.port)).browserServer;
+  async launchServer(options: ServerOptions = {}): Promise<BrowserServer> {
+    return (await this._launchServer(options, 'server', undefined, options.port)).browserServer;
   }
 
-  async launchPersistentContext(userDataDir: string, options?: LaunchOptions): Promise<BrowserContext> {
-    const { timeout = 30000 } = options || {};
+  async launchPersistentContext(userDataDir: string, options: LaunchOptions = {}): Promise<BrowserContext> {
+    const {
+      timeout = 30000,
+      slowMo = undefined
+    } = options;
     const { transport } = await this._launchServer(options, 'persistent', userDataDir);
-    const browser = await CRBrowser.connect(transport!, true);
+    const browser = await CRBrowser.connect(transport!, true, slowMo);
     await helper.waitWithTimeout(browser._firstPagePromise, 'first page', timeout);
     return browser._defaultContext;
   }
 
-  private async _launchServer(options: LaunchOptions = {}, launchType: LaunchType, userDataDir?: string, port?: number): Promise<{ browserServer: BrowserServer, transport?: ConnectionTransport }> {
+  private async _launchServer(options: ProcessOptions, launchType: LaunchType, userDataDir?: string, port?: number): Promise<{ browserServer: BrowserServer, transport?: ConnectionTransport }> {
     const {
       ignoreDefaultArgs = false,
       args = [],
diff --git a/src/server/firefox.ts b/src/server/firefox.ts
index ba0cb663590e6c..af8641017bc6df 100644
--- a/src/server/firefox.ts
+++ b/src/server/firefox.ts
@@ -19,16 +19,16 @@ import * as fs from 'fs';
 import * as os from 'os';
 import * as path from 'path';
 import * as ws from 'ws';
-import { ConnectOptions, LaunchType } from '../browser';
+import { LaunchType } from '../browser';
 import { BrowserContext } from '../browserContext';
 import { TimeoutError } from '../errors';
 import { Events } from '../events';
 import { FFBrowser } from '../firefox/ffBrowser';
 import { kBrowserCloseMessageId } from '../firefox/ffConnection';
-import { debugError, helper } from '../helper';
+import { debugError, helper, assert } from '../helper';
 import * as platform from '../platform';
 import { BrowserServer, WebSocketWrapper } from './browserServer';
-import { BrowserArgOptions, BrowserType, LaunchOptions } from './browserType';
+import { BrowserArgOptions, BrowserType, LaunchOptions, ServerOptions, ProcessOptions, ConnectOptions } from './browserType';
 import { launchProcess, waitForLine } from './processLauncher';
 import { ConnectionTransport, SequenceNumberMixer } from '../transport';
 
@@ -47,12 +47,11 @@ export class Firefox implements BrowserType<FFBrowser> {
     return 'firefox';
   }
 
-  async launch(options?: LaunchOptions & { slowMo?: number }): Promise<FFBrowser> {
-    if (options && (options as any).userDataDir)
-      throw new Error('userDataDir option is not supported in `browserType.launch`. Use `browserType.launchPersistentContext` instead');
+  async launch(options: LaunchOptions = {}): Promise<FFBrowser> {
+    assert(!(options as any).userDataDir, 'userDataDir option is not supported in `browserType.launch`. Use `browserType.launchPersistentContext` instead');
     const browserServer = await this._launchServer(options, 'local');
     const browser = await platform.connectToWebsocket(browserServer.wsEndpoint()!, transport => {
-      return FFBrowser.connect(transport, false, options && options.slowMo);
+      return FFBrowser.connect(transport, false, options.slowMo);
     });
     // Hack: for typical launch scenario, ensure that close waits for actual process termination.
     browser.close = () => browserServer.close();
@@ -60,15 +59,18 @@ export class Firefox implements BrowserType<FFBrowser> {
     return browser;
   }
 
-  async launchServer(options?: LaunchOptions & { port?: number }): Promise<BrowserServer> {
-    return await this._launchServer(options, 'server', undefined, options && options.port);
+  async launchServer(options: ServerOptions = {}): Promise<BrowserServer> {
+    return await this._launchServer(options, 'server', undefined, options.port);
   }
 
-  async launchPersistentContext(userDataDir: string, options?: LaunchOptions): Promise<BrowserContext> {
-    const { timeout = 30000 } = options || {};
+  async launchPersistentContext(userDataDir: string, options: LaunchOptions = {}): Promise<BrowserContext> {
+    const {
+      timeout = 30000,
+      slowMo = undefined,
+    } = options;
     const browserServer = await this._launchServer(options, 'persistent', userDataDir);
     const browser = await platform.connectToWebsocket(browserServer.wsEndpoint()!, transport => {
-      return FFBrowser.connect(transport, true);
+      return FFBrowser.connect(transport, true, slowMo);
     });
     await helper.waitWithTimeout(browser._firstPagePromise, 'first page', timeout);
     // Hack: for typical launch scenario, ensure that close waits for actual process termination.
@@ -77,7 +79,7 @@ export class Firefox implements BrowserType<FFBrowser> {
     return browserContext;
   }
 
-  private async _launchServer(options: LaunchOptions = {}, launchType: LaunchType, userDataDir?: string, port?: number): Promise<BrowserServer> {
+  private async _launchServer(options: ProcessOptions, launchType: LaunchType, userDataDir?: string, port?: number): Promise<BrowserServer> {
     const {
       ignoreDefaultArgs = false,
       args = [],
diff --git a/src/server/webkit.ts b/src/server/webkit.ts
index 1027a497992305..745c87c8f69873 100644
--- a/src/server/webkit.ts
+++ b/src/server/webkit.ts
@@ -22,12 +22,12 @@ import * as fs from 'fs';
 import * as path from 'path';
 import * as platform from '../platform';
 import * as os from 'os';
-import { debugError, helper } from '../helper';
+import { debugError, helper, assert } from '../helper';
 import { kBrowserCloseMessageId } from '../webkit/wkConnection';
-import { LaunchOptions, BrowserArgOptions, BrowserType } from './browserType';
+import { LaunchOptions, BrowserArgOptions, BrowserType, ProcessOptions, ServerOptions, ConnectOptions } from './browserType';
 import { ConnectionTransport, SequenceNumberMixer } from '../transport';
 import * as ws from 'ws';
-import { ConnectOptions, LaunchType } from '../browser';
+import { LaunchType } from '../browser';
 import { BrowserServer, WebSocketWrapper } from './browserServer';
 import { Events } from '../events';
 import { BrowserContext } from '../browserContext';
@@ -45,28 +45,30 @@ export class WebKit implements BrowserType<WKBrowser> {
     return 'webkit';
   }
 
-  async launch(options?: LaunchOptions & { slowMo?: number }): Promise<WKBrowser> {
-    if (options && (options as any).userDataDir)
-      throw new Error('userDataDir option is not supported in `browserType.launch`. Use `browserType.launchPersistentContext` instead');
+  async launch(options: LaunchOptions = {}): Promise<WKBrowser> {
+    assert(!(options as any).userDataDir, 'userDataDir option is not supported in `browserType.launch`. Use `browserType.launchPersistentContext` instead');
     const { browserServer, transport } = await this._launchServer(options, 'local');
-    const browser = await WKBrowser.connect(transport!, options && options.slowMo);
+    const browser = await WKBrowser.connect(transport!, options.slowMo);
     (browser as any)['__server__'] = browserServer;
     return browser;
   }
 
-  async launchServer(options?: LaunchOptions & { port?: number }): Promise<BrowserServer> {
-    return (await this._launchServer(options, 'server', undefined, options && options.port)).browserServer;
+  async launchServer(options: ServerOptions = {}): Promise<BrowserServer> {
+    return (await this._launchServer(options, 'server', undefined, options.port)).browserServer;
   }
 
-  async launchPersistentContext(userDataDir: string, options?: LaunchOptions): Promise<BrowserContext> {
-    const { timeout = 30000 } = options || {};
+  async launchPersistentContext(userDataDir: string, options: LaunchOptions = {}): Promise<BrowserContext> {
+    const {
+      timeout = 30000,
+      slowMo = undefined,
+    } = options || {};
     const { transport } = await this._launchServer(options, 'persistent', userDataDir);
-    const browser = await WKBrowser.connect(transport!, undefined, true);
+    const browser = await WKBrowser.connect(transport!, slowMo, true);
     await helper.waitWithTimeout(browser._waitForFirstPageTarget(), 'first page', timeout);
     return browser._defaultContext;
   }
 
-  private async _launchServer(options: LaunchOptions = {}, launchType: LaunchType, userDataDir?: string, port?: number): Promise<{ browserServer: BrowserServer, transport?: ConnectionTransport }> {
+  private async _launchServer(options: ProcessOptions, launchType: LaunchType, userDataDir?: string, port?: number): Promise<{ browserServer: BrowserServer, transport?: ConnectionTransport }> {
     const {
       ignoreDefaultArgs = false,
       args = [],
diff --git a/test/launcher.spec.js b/test/launcher.spec.js
index b954e67b27de91..eb6defcaff0b68 100644
--- a/test/launcher.spec.js
+++ b/test/launcher.spec.js
@@ -39,7 +39,7 @@ module.exports.describe = function({testRunner, expect, defaultBrowserOptions, p
         await neverResolves;
         expect(error.message).toContain('Protocol error');
       });
-      it('should throw if userDataDir option is passed', async() => {
+      fit('should throw if userDataDir option is passed', async() => {
         let waitError = null;
         const options = Object.assign({}, defaultBrowserOptions, {userDataDir: 'random-path'});
         await browserType.launch(options).catch(e => waitError = e);