diff --git a/packages/injected/src/injectedScript.ts b/packages/injected/src/injectedScript.ts
index c644f99353..cc32237827 100644
--- a/packages/injected/src/injectedScript.ts
+++ b/packages/injected/src/injectedScript.ts
@@ -44,6 +44,7 @@ import type { LayoutSelectorName } from './layoutSelectorUtils';
 import type { SelectorEngine, SelectorRoot } from './selectorEngine';
 import type { GenerateSelectorOptions } from './selectorGenerator';
 import type { ElementText, TextMatcher } from './selectorUtils';
+import type { Builtins } from '@isomorphic/builtins';
 
 
 export type FrameExpectParams = Omit<channels.FrameExpectParams, 'expectedValue'> & { expectedValue?: any };
@@ -64,6 +65,18 @@ interface WebKitLegacyDeviceMotionEvent extends DeviceMotionEvent {
   readonly initDeviceMotionEvent: (type: string, bubbles: boolean, cancelable: boolean, acceleration: DeviceMotionEventAcceleration, accelerationIncludingGravity: DeviceMotionEventAcceleration, rotationRate: DeviceMotionEventRotationRate, interval: number) => void;
 }
 
+export type InjectedScriptOptions = {
+  isUnderTest: boolean;
+  sdkLanguage: Language;
+  // For strict error and codegen
+  testIdAttributeName: string;
+  stableRafCount: number;
+  browserName: string;
+  inputFileRoleTextbox: boolean;
+  customEngines: { name: string, source: string }[];
+  runtimeGuid: string;
+};
+
 export class InjectedScript {
   private _engines: Map<string, SelectorEngine>;
   readonly _evaluator: SelectorEvaluatorImpl;
@@ -96,7 +109,7 @@ export class InjectedScript {
     isInsideScope,
     normalizeWhiteSpace,
     parseAriaSnapshot,
-    builtins: builtins(),
+    builtins: null as unknown as Builtins,
   };
 
   private _autoClosingTags: Set<string>;
@@ -108,15 +121,15 @@ export class InjectedScript {
   private _allHitTargetInterceptorEvents: Set<string>;
 
   // eslint-disable-next-line no-restricted-globals
-  constructor(window: Window & typeof globalThis, isUnderTest: boolean, sdkLanguage: Language, testIdAttributeNameForStrictErrorAndConsoleCodegen: string, stableRafCount: number, browserName: string, inputFileRoleTextbox: boolean, customEngines: { name: string, engine: SelectorEngine }[]) {
+  constructor(window: Window & typeof globalThis, options: InjectedScriptOptions) {
     this.window = window;
     this.document = window.document;
-    this.isUnderTest = isUnderTest;
+    this.isUnderTest = options.isUnderTest;
     // Make sure builtins are created from "window". This is important for InjectedScript instantiated
     // inside a trace viewer snapshot, where "window" differs from "globalThis".
-    this.utils.builtins = builtins(window);
-    this._sdkLanguage = sdkLanguage;
-    this._testIdAttributeNameForStrictErrorAndConsoleCodegen = testIdAttributeNameForStrictErrorAndConsoleCodegen;
+    this.utils.builtins = builtins(options.runtimeGuid, window);
+    this._sdkLanguage = options.sdkLanguage;
+    this._testIdAttributeNameForStrictErrorAndConsoleCodegen = options.testIdAttributeName;
     this._evaluator = new SelectorEvaluatorImpl();
     this.consoleApi = new ConsoleAPI(this);
 
@@ -216,17 +229,17 @@ export class InjectedScript {
     this._engines.set('internal:role', createRoleEngine(true));
     this._engines.set('aria-ref', this._createAriaIdEngine());
 
-    for (const { name, engine } of customEngines)
-      this._engines.set(name, engine);
+    for (const { name, source } of options.customEngines)
+      this._engines.set(name, this.eval(source));
 
-    this._stableRafCount = stableRafCount;
-    this._browserName = browserName;
-    setGlobalOptions({ browserNameForWorkarounds: browserName, inputFileRoleTextbox });
+    this._stableRafCount = options.stableRafCount;
+    this._browserName = options.browserName;
+    setGlobalOptions({ browserNameForWorkarounds: options.browserName, inputFileRoleTextbox: options.inputFileRoleTextbox });
 
     this._setupGlobalListenersRemovalDetection();
     this._setupHitTargetInterceptors();
 
-    if (isUnderTest)
+    if (options.isUnderTest)
       (this.window as any).__injectedScript = this;
   }
 
diff --git a/packages/injected/src/utilityScript.ts b/packages/injected/src/utilityScript.ts
index a2526f98db..e07733076f 100644
--- a/packages/injected/src/utilityScript.ts
+++ b/packages/injected/src/utilityScript.ts
@@ -17,13 +17,19 @@
 import { builtins } from '@isomorphic/builtins';
 import { source } from '@isomorphic/utilityScriptSerializers';
 
+import type { Builtins } from '@isomorphic/builtins';
+
 export class UtilityScript {
-  constructor(isUnderTest: boolean) {
+
+  private _builtins: Builtins;
+
+  constructor(runtimeGuid: string, isUnderTest: boolean) {
     if (isUnderTest) {
       // eslint-disable-next-line no-restricted-globals
-      (globalThis as any).builtins = builtins();
+      (globalThis as any).builtins = builtins(runtimeGuid);
     }
-    const result = source(builtins());
+    this._builtins = builtins(runtimeGuid);
+    const result = source(this._builtins);
     this.serializeAsCallArgument = result.serializeAsCallArgument;
     this.parseEvaluationResultValue = result.parseEvaluationResultValue;
   }
@@ -38,7 +44,7 @@ export class UtilityScript {
     for (let i = 0; i < args.length; i++)
       parameters[i] = this.parseEvaluationResultValue(args[i], handles);
 
-    let result = builtins().eval(expression);
+    let result = this._builtins.eval(expression);
     if (isFunction === true) {
       result = result(...parameters);
     } else if (isFunction === false) {
diff --git a/packages/playwright-core/src/server/bidi/bidiPage.ts b/packages/playwright-core/src/server/bidi/bidiPage.ts
index 76267ab89c..50e45d1352 100644
--- a/packages/playwright-core/src/server/bidi/bidiPage.ts
+++ b/packages/playwright-core/src/server/bidi/bidiPage.ts
@@ -19,7 +19,7 @@ import { eventsHelper } from '../utils/eventsHelper';
 import { BrowserContext } from '../browserContext';
 import * as dialog from '../dialog';
 import * as dom from '../dom';
-import { Page } from '../page';
+import { Page, PageBinding } from '../page';
 import { BidiExecutionContext, createHandle } from './bidiExecutionContext';
 import { RawKeyboardImpl, RawMouseImpl, RawTouchscreenImpl } from './bidiInput';
 import { BidiNetworkManager } from './bidiNetworkManager';
@@ -573,7 +573,7 @@ export class BidiPage implements PageDelegate {
 }
 
 export function addMainBinding(callback: (arg: any) => void) {
-  (globalThis as any)['__playwright__binding__'] = callback;
+  (globalThis as any)[PageBinding.kPlaywrightBinding] = callback;
 }
 
 function toBidiExecutionContext(executionContext: dom.FrameExecutionContext): BidiExecutionContext {
diff --git a/packages/playwright-core/src/server/browserContext.ts b/packages/playwright-core/src/server/browserContext.ts
index 46bc5ad7b9..1c44ac2987 100644
--- a/packages/playwright-core/src/server/browserContext.ts
+++ b/packages/playwright-core/src/server/browserContext.ts
@@ -28,7 +28,7 @@ import { mkdirIfNeeded } from './utils/fileUtils';
 import { HarRecorder } from './har/harRecorder';
 import { helper } from './helper';
 import { SdkObject, serverSideCallMetadata } from './instrumentation';
-import { builtins } from '../utils/isomorphic/builtins';
+import { builtinsSource } from '../utils/isomorphic/builtins';
 import * as utilityScriptSerializers from '../utils/isomorphic/utilityScriptSerializers';
 import * as network from './network';
 import { InitScript } from './page';
@@ -37,6 +37,7 @@ import { Recorder } from './recorder';
 import { RecorderApp } from './recorder/recorderApp';
 import * as storageScript from './storageScript';
 import { Tracing } from './trace/recorder/tracing';
+import * as js from './javascript';
 
 import type { Artifact } from './artifact';
 import type { Browser, BrowserOptions } from './browser';
@@ -518,7 +519,7 @@ export abstract class BrowserContext extends SdkObject {
     };
     const originsToSave = new Set(this._origins);
 
-    const collectScript = `(${storageScript.collect})(${utilityScriptSerializers.source}, (${builtins})(), ${this._browser.options.name === 'firefox'}, ${indexedDB})`;
+    const collectScript = `(${storageScript.collect})(${utilityScriptSerializers.source}, ${builtinsSource(js.runtimeGuid)}, ${this._browser.options.name === 'firefox'}, ${indexedDB})`;
 
     // First try collecting storage stage from existing pages.
     for (const page of this.pages()) {
@@ -611,7 +612,7 @@ export abstract class BrowserContext extends SdkObject {
         for (const originState of state.origins) {
           const frame = page.mainFrame();
           await frame.goto(metadata, originState.origin);
-          await frame.evaluateExpression(`(${storageScript.restore})(${utilityScriptSerializers.source}, (${builtins})(), ${JSON.stringify(originState)})`, { world: 'utility' });
+          await frame.evaluateExpression(`(${storageScript.restore})(${utilityScriptSerializers.source}, ${builtinsSource(js.runtimeGuid)}, ${JSON.stringify(originState)})`, { world: 'utility' });
         }
         await page.close(internalMetadata);
       }
diff --git a/packages/playwright-core/src/server/dom.ts b/packages/playwright-core/src/server/dom.ts
index 0886ad9195..a859c7992f 100644
--- a/packages/playwright-core/src/server/dom.ts
+++ b/packages/playwright-core/src/server/dom.ts
@@ -24,7 +24,7 @@ import { isSessionClosedError } from './protocolError';
 import * as injectedScriptSource from '../generated/injectedScriptSource';
 
 import type * as frames from './frames';
-import type { ElementState, HitTargetInterceptionResult, InjectedScript } from '@injected/injectedScript';
+import type { ElementState, HitTargetInterceptionResult, InjectedScript, InjectedScriptOptions } from '@injected/injectedScript';
 import type { CallMetadata } from './instrumentation';
 import type { Page } from './page';
 import type { Progress } from './progress';
@@ -85,25 +85,26 @@ export class FrameExecutionContext extends js.ExecutionContext {
 
   injectedScript(): Promise<js.JSHandle<InjectedScript>> {
     if (!this._injectedScriptPromise) {
-      const custom: string[] = [];
+      const customEngines: InjectedScriptOptions['customEngines'] = [];
       const selectorsRegistry = this.frame._page.context().selectors();
       for (const [name, { source }] of selectorsRegistry._engines)
-        custom.push(`{ name: '${name}', engine: (${source}) }`);
+        customEngines.push({ name, source });
       const sdkLanguage = this.frame.attribution.playwright.options.sdkLanguage;
+      const options: InjectedScriptOptions = {
+        isUnderTest: isUnderTest(),
+        sdkLanguage,
+        testIdAttributeName: selectorsRegistry.testIdAttributeName(),
+        stableRafCount: this.frame._page._delegate.rafCountForStablePosition(),
+        browserName: this.frame._page._browserContext._browser.options.name,
+        inputFileRoleTextbox: process.env.PLAYWRIGHT_INPUT_FILE_TEXTBOX ? true : false,
+        customEngines,
+        runtimeGuid: js.runtimeGuid,
+      };
       const source = `
         (() => {
         const module = {};
         ${injectedScriptSource.source}
-        return new (module.exports.InjectedScript())(
-          globalThis,
-          ${isUnderTest()},
-          "${sdkLanguage}",
-          ${JSON.stringify(selectorsRegistry.testIdAttributeName())},
-          ${this.frame._page._delegate.rafCountForStablePosition()},
-          "${this.frame._page._browserContext._browser.options.name}",
-          ${process.env.PLAYWRIGHT_INPUT_FILE_TEXTBOX ? 'true' : 'false'},
-          [${custom.join(',\n')}]
-        );
+        return new (module.exports.InjectedScript())(globalThis, ${JSON.stringify(options)});
         })();
       `;
       this._injectedScriptPromise = this.rawEvaluateHandle(source)
diff --git a/packages/playwright-core/src/server/javascript.ts b/packages/playwright-core/src/server/javascript.ts
index 4413c3f19e..0fce67c26f 100644
--- a/packages/playwright-core/src/server/javascript.ts
+++ b/packages/playwright-core/src/server/javascript.ts
@@ -16,7 +16,7 @@
 
 import { SdkObject } from './instrumentation';
 import * as utilityScriptSource from '../generated/utilityScriptSource';
-import { isUnderTest } from '../utils';
+import { createGuid, isUnderTest } from '../utils';
 import { builtins } from '../utils/isomorphic/builtins';
 import { source } from '../utils/isomorphic/utilityScriptSerializers';
 import { LongStandingScope } from '../utils/isomorphic/manualPromise';
@@ -24,6 +24,9 @@ import { LongStandingScope } from '../utils/isomorphic/manualPromise';
 import type * as dom from './dom';
 import type { UtilityScript } from '@injected/utilityScript';
 
+// Use in the web-facing names to avoid leaking Playwright to the pages.
+export const runtimeGuid = createGuid();
+
 interface TaggedAsJSHandle<T> {
   __jshandle: T;
 }
@@ -46,7 +49,7 @@ export type Func1<Arg, R> = string | ((arg: Unboxed<Arg>) => R | Promise<R>);
 export type FuncOn<On, Arg2, R> = string | ((on: On, arg2: Unboxed<Arg2>) => R | Promise<R>);
 export type SmartHandle<T> = T extends Node ? dom.ElementHandle<T> : JSHandle<T>;
 
-const utilityScriptSerializers = source(builtins());
+const utilityScriptSerializers = source(builtins(runtimeGuid));
 export const parseEvaluationResultValue = utilityScriptSerializers.parseEvaluationResultValue;
 export const serializeAsCallArgument = utilityScriptSerializers.serializeAsCallArgument;
 
@@ -109,7 +112,7 @@ export class ExecutionContext extends SdkObject {
       (() => {
         const module = {};
         ${utilityScriptSource.source}
-        return new (module.exports.UtilityScript())(${isUnderTest()});
+        return new (module.exports.UtilityScript())(${JSON.stringify(runtimeGuid)}, ${isUnderTest()});
       })();`;
       this._utilityScriptPromise = this._raceAgainstContextDestroyed(this.delegate.rawEvaluateHandle(this, source))
           .then(handle => {
diff --git a/packages/playwright-core/src/server/page.ts b/packages/playwright-core/src/server/page.ts
index d10a638e6c..4e739c6493 100644
--- a/packages/playwright-core/src/server/page.ts
+++ b/packages/playwright-core/src/server/page.ts
@@ -24,7 +24,7 @@ import * as frames from './frames';
 import { helper } from './helper';
 import * as input from './input';
 import { SdkObject } from './instrumentation';
-import { builtins } from '../utils/isomorphic/builtins';
+import { builtinsSource } from '../utils/isomorphic/builtins';
 import { createPageBindingScript, deliverBindingResult, takeBindingHandle } from './pageBinding';
 import * as js from './javascript';
 import { ProgressController } from './progress';
@@ -858,7 +858,7 @@ export class Worker extends SdkObject {
 }
 
 export class PageBinding {
-  static kPlaywrightBinding = '__playwright__binding__';
+  static kPlaywrightBinding = '__playwright__binding__' + js.runtimeGuid;
 
   readonly name: string;
   readonly playwrightFunction: frames.FunctionWithSource;
@@ -906,11 +906,15 @@ export class InitScript {
   constructor(source: string, internal?: boolean, name?: string) {
     const guid = createGuid();
     this.source = `(() => {
-      globalThis.__pwInitScripts = globalThis.__pwInitScripts || {};
-      const hasInitScript = globalThis.__pwInitScripts[${JSON.stringify(guid)}];
+      const name = '__pw_init_scripts__${js.runtimeGuid}';
+      if (!globalThis[name])
+        Object.defineProperty(globalThis, name, { value: {}, configurable: false, enumerable: false, writable: false });
+
+      const globalInitScripts = globalThis[name];
+      const hasInitScript = globalInitScripts[${JSON.stringify(guid)}];
       if (hasInitScript)
         return;
-      globalThis.__pwInitScripts[${JSON.stringify(guid)}] = true;
+      globalThis[name][${JSON.stringify(guid)}] = true;
       ${source}
     })();`;
     this.internal = !!internal;
@@ -918,7 +922,7 @@ export class InitScript {
   }
 }
 
-export const kBuiltinsScript = new InitScript(`(${builtins})()`, true /* internal */);
+export const kBuiltinsScript = new InitScript(builtinsSource(js.runtimeGuid), true /* internal */);
 
 class FrameThrottler {
   private _acks: (() => void)[] = [];
diff --git a/packages/playwright-core/src/server/pageBinding.ts b/packages/playwright-core/src/server/pageBinding.ts
index 0e7f1da8d6..a1910b9f6a 100644
--- a/packages/playwright-core/src/server/pageBinding.ts
+++ b/packages/playwright-core/src/server/pageBinding.ts
@@ -14,8 +14,9 @@
  * limitations under the License.
  */
 
-import { builtins } from '../utils/isomorphic/builtins';
+import { builtinsSource } from '../utils/isomorphic/builtins';
 import { source } from '../utils/isomorphic/utilityScriptSerializers';
+import * as js from './javascript';
 
 import type { Builtins } from '../utils/isomorphic/builtins';
 import type { SerializedValue } from '../utils/isomorphic/utilityScriptSerializers';
@@ -88,5 +89,5 @@ export function deliverBindingResult(arg: { name: string, seq: number, result?:
 }
 
 export function createPageBindingScript(playwrightBinding: string, name: string, needsHandle: boolean) {
-  return `(${addPageBinding.toString()})(${JSON.stringify(playwrightBinding)}, ${JSON.stringify(name)}, ${needsHandle}, (${source}), (${builtins})())`;
+  return `(${addPageBinding.toString()})(${JSON.stringify(playwrightBinding)}, ${JSON.stringify(name)}, ${needsHandle}, (${source}), ${builtinsSource(js.runtimeGuid)})`;
 }
diff --git a/packages/playwright-core/src/utils/isomorphic/builtins.ts b/packages/playwright-core/src/utils/isomorphic/builtins.ts
index 7a4d2502b6..fa80287cf4 100644
--- a/packages/playwright-core/src/utils/isomorphic/builtins.ts
+++ b/packages/playwright-core/src/utils/isomorphic/builtins.ts
@@ -41,31 +41,39 @@ export type Builtins = {
 // anything else happens in the page. This way, original builtins are saved on the global object
 // before page can temper with them. Later on, any call to builtins() will retrieve the stored
 // builtins instead of initializing them again.
-export function builtins(global?: typeof globalThis): Builtins {
+export function builtins(runtimeGuid: string, global?: typeof globalThis): Builtins {
   global = global ?? globalThis;
-  if (!(global as any)['__playwright_builtins__']) {
-    const builtins: Builtins = {
-      setTimeout: global.setTimeout?.bind(global),
-      clearTimeout: global.clearTimeout?.bind(global),
-      setInterval: global.setInterval?.bind(global),
-      clearInterval: global.clearInterval?.bind(global),
-      requestAnimationFrame: global.requestAnimationFrame?.bind(global),
-      cancelAnimationFrame: global.cancelAnimationFrame?.bind(global),
-      requestIdleCallback: global.requestIdleCallback?.bind(global),
-      cancelIdleCallback: global.cancelIdleCallback?.bind(global),
-      performance: global.performance,
-      eval: global.eval?.bind(global),
-      Intl: global.Intl,
-      Date: global.Date,
-      Map: global.Map,
-      Set: global.Set,
-    };
-    Object.defineProperty(global, '__playwright_builtins__', { value: builtins, configurable: false, enumerable: false, writable: false });
-  }
-  return (global as any)['__playwright_builtins__'];
+  const name = `__playwright_builtins__${runtimeGuid}`;
+  let builtins: Builtins = (global as any)[name];
+  if (builtins)
+    return builtins;
+
+  builtins = {
+    setTimeout: global.setTimeout?.bind(global),
+    clearTimeout: global.clearTimeout?.bind(global),
+    setInterval: global.setInterval?.bind(global),
+    clearInterval: global.clearInterval?.bind(global),
+    requestAnimationFrame: global.requestAnimationFrame?.bind(global),
+    cancelAnimationFrame: global.cancelAnimationFrame?.bind(global),
+    requestIdleCallback: global.requestIdleCallback?.bind(global),
+    cancelIdleCallback: global.cancelIdleCallback?.bind(global),
+    performance: global.performance,
+    eval: global.eval?.bind(global),
+    Intl: global.Intl,
+    Date: global.Date,
+    Map: global.Map,
+    Set: global.Set,
+  };
+  if (runtimeGuid)
+    Object.defineProperty(global, name, { value: builtins, configurable: false, enumerable: false, writable: false });
+  return builtins;
 }
 
-const instance = builtins();
+export function builtinsSource(runtimeGuid: string): string {
+  return `(${builtins})(${JSON.stringify(runtimeGuid)})`;
+}
+
+const instance = builtins('');
 export const setTimeout = instance.setTimeout;
 export const clearTimeout = instance.clearTimeout;
 export const setInterval = instance.setInterval;
diff --git a/packages/trace-viewer/src/ui/snapshotTab.tsx b/packages/trace-viewer/src/ui/snapshotTab.tsx
index 7211aa9e2e..de4d4bb4e0 100644
--- a/packages/trace-viewer/src/ui/snapshotTab.tsx
+++ b/packages/trace-viewer/src/ui/snapshotTab.tsx
@@ -77,7 +77,7 @@ export const SnapshotTabsView: React.FunctionComponent<{
       <ToolbarButton icon='link-external' title='Open snapshot in a new tab' disabled={!snapshotUrls?.popoutUrl} onClick={() => {
         const win = window.open(snapshotUrls?.popoutUrl || '', '_blank');
         win?.addEventListener('DOMContentLoaded', () => {
-          const injectedScript = new InjectedScript(win as any, false, sdkLanguage, testIdAttributeName, 1, 'chromium', false, []);
+          const injectedScript = new InjectedScript(win as any, { isUnderTest: false, sdkLanguage, testIdAttributeName, stableRafCount: 1, browserName: 'chromium', inputFileRoleTextbox: false, customEngines: [], runtimeGuid: '' });
           injectedScript.consoleApi.install();
         });
       }} />
@@ -280,7 +280,7 @@ function createRecorders(recorders: { recorder: Recorder, frameSelector: string
     return;
   const win = frameWindow as any;
   if (!win._recorder) {
-    const injectedScript = new InjectedScript(frameWindow as any, isUnderTest, sdkLanguage, testIdAttributeName, 1, 'chromium', false, []);
+    const injectedScript = new InjectedScript(frameWindow as any, { isUnderTest, sdkLanguage, testIdAttributeName, stableRafCount: 1, browserName: 'chromium', inputFileRoleTextbox: false, customEngines: [], runtimeGuid: '' });
     const recorder = new Recorder(injectedScript);
     win._injectedScript = injectedScript;
     win._recorder = { recorder, frameSelector: parentFrameSelector };