diff --git a/juggler/BrowserContextManager.js b/juggler/BrowserContextManager.js
index 3365aa61871830..bd57d338c279f5 100644
--- a/juggler/BrowserContextManager.js
+++ b/juggler/BrowserContextManager.js
@@ -83,6 +83,7 @@ class BrowserContext {
     this._manager._userContextIdToBrowserContext.set(this.userContextId, this);
     this.options = options || {};
     this.options.scriptsToEvaluateOnNewDocument = [];
+    this.options.bindings = [];
     this.pages = new Set();
   }
 
@@ -100,6 +101,11 @@ class BrowserContext {
     await Promise.all(Array.from(this.pages).map(page => page.addScriptToEvaluateOnNewDocument(script)));
   }
 
+  async addBinding(name, script) {
+    this.options.bindings.push({ name, script });
+    await Promise.all(Array.from(this.pages).map(page => page.addBinding(name, script)));
+  }
+
   async setGeolocationOverride(geolocation) {
     this.options.geolocation = geolocation;
     await Promise.all(Array.from(this.pages).map(page => page.setGeolocationOverride(geolocation)));
diff --git a/juggler/TargetRegistry.js b/juggler/TargetRegistry.js
index 75ea79a8fa493f..e624e3c21a20dd 100644
--- a/juggler/TargetRegistry.js
+++ b/juggler/TargetRegistry.js
@@ -234,6 +234,10 @@ class PageTarget {
     await this._channel.connect('').send('addScriptToEvaluateOnNewDocument', script).catch(e => void e);
   }
 
+  async addBinding(name, script) {
+    await this._channel.connect('').send('addBinding', { name, script }).catch(e => void e);
+  }
+
   async setGeolocationOverride(geolocation) {
     await this._channel.connect('').send('setGeolocationOverride', geolocation).catch(e => void e);
   }
diff --git a/juggler/content/FrameTree.js b/juggler/content/FrameTree.js
index 13c3cd817b369e..679b5851c42706 100644
--- a/juggler/content/FrameTree.js
+++ b/juggler/content/FrameTree.js
@@ -18,6 +18,7 @@ class FrameTree {
       this._browsingContextGroup.__jugglerFrameTrees = new Set();
     this._browsingContextGroup.__jugglerFrameTrees.add(this);
 
+    this._bindings = new Map();
     this._workers = new Map();
     this._docShellToFrame = new Map();
     this._frameIdToFrame = new Map();
@@ -48,6 +49,7 @@ class FrameTree {
     this._eventListeners = [
       helper.addObserver(subject => this._onDocShellCreated(subject.QueryInterface(Ci.nsIDocShell)), 'webnavigation-create'),
       helper.addObserver(subject => this._onDocShellDestroyed(subject.QueryInterface(Ci.nsIDocShell)), 'webnavigation-destroy'),
+      helper.addObserver(window => this._onDOMWindowCreated(window), 'content-document-global-created'),
       helper.addProgressListener(webProgress, this, flags),
     ];
   }
@@ -111,6 +113,25 @@ class FrameTree {
     return this._scriptsToEvaluateOnNewDocument;
   }
 
+  addBinding(name, script) {
+    this._bindings.set(name, script);
+    for (const frame of this.frames())
+      this._addBindingToFrame(frame, name, script);
+  }
+
+  _addBindingToFrame(frame, name, script) {
+    Cu.exportFunction((...args) => {
+      this.emit(FrameTree.Events.BindingCalled, {
+        frame,
+        name,
+        payload: args[0]
+      });
+    }, frame.domWindow(), {
+      defineAs: name,
+    });
+    frame.domWindow().eval(script);
+  }
+
   frameForDocShell(docShell) {
     return this._docShellToFrame.get(docShell) || null;
   }
@@ -218,6 +239,8 @@ class FrameTree {
     const frame = new Frame(this, docShell, parentFrame);
     this._docShellToFrame.set(docShell, frame);
     this._frameIdToFrame.set(frame.id(), frame);
+    for (const [name, script] of this._bindings)
+      this._addBindingToFrame(frame, name, script);
     this.emit(FrameTree.Events.FrameAttached, frame);
     return frame;
   }
@@ -228,6 +251,16 @@ class FrameTree {
       this._detachFrame(frame);
   }
 
+  _onDOMWindowCreated(window) {
+    const docShell = window.docShell;
+    const frame = this.frameForDocShell(docShell);
+    if (!frame)
+      return;
+    for (const [name, script] of this._bindings)
+      this._addBindingToFrame(frame, name, script);
+    this.emit(FrameTree.Events.GlobalObjectCreated, { frame, window });
+  }
+
   _detachFrame(frame) {
     // Detach all children first
     for (const subframe of frame._children)
@@ -242,8 +275,10 @@ class FrameTree {
 }
 
 FrameTree.Events = {
+  BindingCalled: 'bindingcalled',
   FrameAttached: 'frameattached',
   FrameDetached: 'framedetached',
+  GlobalObjectCreated: 'globalobjectcreated',
   WorkerCreated: 'workercreated',
   WorkerDestroyed: 'workerdestroyed',
   NavigationStarted: 'navigationstarted',
diff --git a/juggler/content/PageAgent.js b/juggler/content/PageAgent.js
index 3dd06f27d071a1..6a001d9f51c819 100644
--- a/juggler/content/PageAgent.js
+++ b/juggler/content/PageAgent.js
@@ -63,8 +63,6 @@ class FrameData {
       name: '',
     });
 
-    for (const bindingName of this._agent._bindingsToAdd.values())
-      this.exposeFunction(bindingName);
     for (const script of this._agent._frameTree.scriptsToEvaluateOnNewDocument()) {
       // TODO: this should actually be handled in FrameTree, but first we have to move
       // execution contexts there.
@@ -86,18 +84,6 @@ class FrameData {
     }
   }
 
-  exposeFunction(name) {
-    Cu.exportFunction((...args) => {
-      this._agent._browserPage.emit('pageBindingCalled', {
-        executionContextId: this.mainContext.id(),
-        name,
-        payload: args[0]
-      });
-    }, this._frame.domWindow(), {
-      defineAs: name,
-    });
-  }
-
   createIsolatedWorld(name) {
     const principal = [this._frame.domWindow()]; // extended principal
     const sandbox = Cu.Sandbox(principal, {
@@ -144,11 +130,10 @@ class PageAgent {
     this._frameData = new Map();
     this._workerData = new Map();
     this._scriptsToEvaluateOnNewDocument = new Map();
-    this._bindingsToAdd = new Set();
 
     this._eventListeners = [
       browserChannel.register(sessionId + 'page', {
-        addBinding: this._addBinding.bind(this),
+        addBinding: ({ name, script }) => this._frameTree.addBinding(name, script),
         addScriptToEvaluateOnNewDocument: this._addScriptToEvaluateOnNewDocument.bind(this),
         adoptNode: this._adoptNode.bind(this),
         awaitViewportDimensions: this._awaitViewportDimensions.bind(this),
@@ -270,13 +255,14 @@ class PageAgent {
       helper.addObserver(this._linkClicked.bind(this, false), 'juggler-link-click'),
       helper.addObserver(this._linkClicked.bind(this, true), 'juggler-link-click-sync'),
       helper.addObserver(this._filePickerShown.bind(this), 'juggler-file-picker-shown'),
-      helper.addObserver(this._onDOMWindowCreated.bind(this), 'content-document-global-created'),
       helper.addEventListener(this._messageManager, 'DOMContentLoaded', this._onDOMContentLoaded.bind(this)),
       helper.addEventListener(this._messageManager, 'pageshow', this._onLoad.bind(this)),
       helper.addObserver(this._onDocumentOpenLoad.bind(this), 'juggler-document-open-loaded'),
       helper.addEventListener(this._messageManager, 'error', this._onError.bind(this)),
+      helper.on(this._frameTree, 'bindingcalled', this._onBindingCalled.bind(this)),
       helper.on(this._frameTree, 'frameattached', this._onFrameAttached.bind(this)),
       helper.on(this._frameTree, 'framedetached', this._onFrameDetached.bind(this)),
+      helper.on(this._frameTree, 'globalobjectcreated', this._onGlobalObjectCreated.bind(this)),
       helper.on(this._frameTree, 'navigationstarted', this._onNavigationStarted.bind(this)),
       helper.on(this._frameTree, 'navigationcommitted', this._onNavigationCommitted.bind(this)),
       helper.on(this._frameTree, 'navigationaborted', this._onNavigationAborted.bind(this)),
@@ -434,11 +420,7 @@ class PageAgent {
     });
   }
 
-  _onDOMWindowCreated(window) {
-    const docShell = window.docShell;
-    const frame = this._frameTree.frameForDocShell(docShell);
-    if (!frame)
-      return;
+  _onGlobalObjectCreated({ frame }) {
     this._frameData.get(frame).reset();
   }
 
@@ -457,6 +439,15 @@ class PageAgent {
     });
   }
 
+  _onBindingCalled({frame, name, payload}) {
+    const frameData = this._frameData.get(frame);
+    this._browserPage.emit('pageBindingCalled', {
+      executionContextId: frameData.mainContext.id(),
+      name,
+      payload
+    });
+  }
+
   dispose() {
     for (const workerData of this._workerData.values())
       workerData.dispose();
@@ -524,14 +515,6 @@ class PageAgent {
     return {navigationId: frame.pendingNavigationId(), navigationURL: frame.pendingNavigationURL()};
   }
 
-  _addBinding({name}) {
-    if (this._bindingsToAdd.has(name))
-      throw new Error(`Binding with name ${name} already exists`);
-    this._bindingsToAdd.add(name);
-    for (const frameData of this._frameData.values())
-      frameData.exposeFunction(name);
-  }
-
   async _adoptNode({frameId, objectId, executionContextId}) {
     const frame = this._frameTree.frame(frameId);
     if (!frame)
diff --git a/juggler/content/main.js b/juggler/content/main.js
index 56472e8515cb84..9bb5c2bff8eb3e 100644
--- a/juggler/content/main.js
+++ b/juggler/content/main.js
@@ -73,7 +73,7 @@ function initialize() {
     response = { sessionIds: [], browserContextOptions: {}, waitForInitialNavigation: false };
 
   const { sessionIds, browserContextOptions, waitForInitialNavigation } = response;
-  const { userAgent, bypassCSP, javaScriptDisabled, viewport, scriptsToEvaluateOnNewDocument, locale, geolocation, onlineOverride } = browserContextOptions;
+  const { userAgent, bypassCSP, javaScriptDisabled, viewport, scriptsToEvaluateOnNewDocument, bindings, locale, geolocation, onlineOverride } = browserContextOptions;
 
   if (userAgent !== undefined)
     docShell.customUserAgent = userAgent;
@@ -97,6 +97,8 @@ function initialize() {
   frameTree = new FrameTree(docShell, waitForInitialNavigation);
   for (const script of scriptsToEvaluateOnNewDocument || [])
     frameTree.addScriptToEvaluateOnNewDocument(script);
+  for (const { name, script } of bindings || [])
+    frameTree.addBinding(name, script);
   networkMonitor = new NetworkMonitor(docShell, frameTree);
 
   const channel = SimpleChannel.createForMessageManager('content::page', messageManager);
@@ -117,6 +119,10 @@ function initialize() {
       frameTree.addScriptToEvaluateOnNewDocument(script);
     },
 
+    addBinding(name, script) {
+      frameTree.addBinding(name, script);
+    },
+
     setGeolocationOverride(geolocation) {
       setGeolocationOverrideInDocShell(geolocation);
     },
diff --git a/juggler/protocol/BrowserHandler.js b/juggler/protocol/BrowserHandler.js
index b3a7b47765d69f..e225fc81c62bbf 100644
--- a/juggler/protocol/BrowserHandler.js
+++ b/juggler/protocol/BrowserHandler.js
@@ -146,6 +146,10 @@ class BrowserHandler {
     await this._contextManager.browserContextForId(browserContextId).addScriptToEvaluateOnNewDocument(script);
   }
 
+  async addBinding({browserContextId, name, script}) {
+    await this._contextManager.browserContextForId(browserContextId).addBinding(name, script);
+  }
+
   setCookies({browserContextId, cookies}) {
     this._contextManager.browserContextForId(browserContextId).setCookies(cookies);
   }
diff --git a/juggler/protocol/Protocol.js b/juggler/protocol/Protocol.js
index 390e68d71c0034..67df4d5592d66e 100644
--- a/juggler/protocol/Protocol.js
+++ b/juggler/protocol/Protocol.js
@@ -273,6 +273,13 @@ const Browser = {
         script: t.String,
       }
     },
+    'addBinding': {
+      params: {
+        browserContextId: t.Optional(t.String),
+        name: t.String,
+        script: t.String,
+      },
+    },
     'grantPermissions': {
       params: {
         origin: t.String,
@@ -559,6 +566,7 @@ const Page = {
     'addBinding': {
       params: {
         name: t.String,
+        script: t.String,
       },
     },
     'setViewportSize': {