diff --git a/browser_patches/firefox/BUILD_NUMBER b/browser_patches/firefox/BUILD_NUMBER
index 01f579d081..03fb4e1920 100644
--- a/browser_patches/firefox/BUILD_NUMBER
+++ b/browser_patches/firefox/BUILD_NUMBER
@@ -1,2 +1,2 @@
-1163
-Changed: yurys@chromium.org Wed Aug 19 15:35:02 PDT 2020
+1164
+Changed: yurys@chromium.org Thu Aug 20 10:30:04 PDT 2020
diff --git a/browser_patches/firefox/juggler/TargetRegistry.js b/browser_patches/firefox/juggler/TargetRegistry.js
index cd47cabe7e..ff857eccbc 100644
--- a/browser_patches/firefox/juggler/TargetRegistry.js
+++ b/browser_patches/firefox/juggler/TargetRegistry.js
@@ -134,8 +134,7 @@ class TargetRegistry {
         if (!target)
           return;
         target.emit('crashed');
-        target.dispose();
-        this.emit(TargetRegistry.Events.TargetDestroyed, target);
+        this._destroyTarget(target).catch(e => dump(`Failed to destroy target: ${e}`));
       }
     }, 'oop-frameloader-crashed');
 
@@ -182,7 +181,6 @@ class TargetRegistry {
         const sessions = [];
         const readyData = { sessions, target };
         this.emit(TargetRegistry.Events.TargetCreated, readyData);
-        sessions.forEach(session => target._initSession(session));
         return {
           scriptsToEvaluateOnNewDocument: browserContext ? browserContext.scriptsToEvaluateOnNewDocument : [],
           bindings: browserContext ? browserContext.bindings : [],
@@ -204,10 +202,7 @@ class TargetRegistry {
       const tab = event.target;
       const linkedBrowser = tab.linkedBrowser;
       const target = this._browserToTarget.get(linkedBrowser);
-      if (target) {
-        target.dispose();
-        this.emit(TargetRegistry.Events.TargetDestroyed, target);
-      }
+      this._destroyTarget(target).catch(e => dump(`Failed to destroy target: ${e}`));
     };
 
     Services.wm.addListener({
@@ -245,6 +240,16 @@ class TargetRegistry {
     extHelperAppSvc.setDownloadInterceptor(new DownloadInterceptor(this));
   }
 
+  async _destroyTarget(target) {
+    if (!target)
+      return;
+    const event = { pendingActivity: [], target };
+    this.emit(TargetRegistry.Events.TargetWillBeDestroyed, event);
+    await Promise.all(event.pendingActivity);
+    target.dispose();
+    this.emit(TargetRegistry.Events.TargetDestroyed, target);
+  }
+
   setBrowserProxy(proxy) {
     this._browserProxy = proxy;
   }
@@ -400,7 +405,6 @@ class PageTarget {
   }
 
   connectSession(session) {
-    this._initSession(session);
     this._channel.connect('').send('attach', { sessionId: session.sessionId() });
   }
 
@@ -415,7 +419,7 @@ class PageTarget {
     });
   }
 
-  _initSession(session) {
+  initSession(session) {
     const pageHandler = new PageHandler(this, session, this._channel);
     const networkHandler = new NetworkHandler(this, session, this._channel);
     session.registerHandler('Page', pageHandler);
@@ -738,6 +742,7 @@ function setViewportSizeForBrowser(viewportSize, browser, window) {
 
 TargetRegistry.Events = {
   TargetCreated: Symbol('TargetRegistry.Events.TargetCreated'),
+  TargetWillBeDestroyed: Symbol('TargetRegistry.Events.TargetWillBeDestroyed'),
   TargetDestroyed: Symbol('TargetRegistry.Events.TargetDestroyed'),
   DownloadCreated: Symbol('TargetRegistry.Events.DownloadCreated'),
   DownloadFinished: Symbol('TargetRegistry.Events.DownloadFinished'),
diff --git a/browser_patches/firefox/juggler/protocol/BrowserHandler.js b/browser_patches/firefox/juggler/protocol/BrowserHandler.js
index 9b960add61..63908ecf1e 100644
--- a/browser_patches/firefox/juggler/protocol/BrowserHandler.js
+++ b/browser_patches/firefox/juggler/protocol/BrowserHandler.js
@@ -33,6 +33,7 @@ class BrowserHandler {
       if (!this._shouldAttachToTarget(target))
         continue;
       const session = this._dispatcher.createSession();
+      target.initSession(session);
       target.connectSession(session);
       this._attachedSessions.set(target, session);
       this._session.emitEvent('Browser.attachedToTarget', {
@@ -43,7 +44,7 @@ class BrowserHandler {
 
     this._eventListeners = [
       helper.on(this._targetRegistry, TargetRegistry.Events.TargetCreated, this._onTargetCreated.bind(this)),
-      helper.on(this._targetRegistry, TargetRegistry.Events.TargetDestroyed, this._onTargetDestroyed.bind(this)),
+      helper.on(this._targetRegistry, TargetRegistry.Events.TargetWillBeDestroyed, this._onTargetWillBeDestroyed.bind(this)),
       helper.on(this._targetRegistry, TargetRegistry.Events.DownloadCreated, this._onDownloadCreated.bind(this)),
       helper.on(this._targetRegistry, TargetRegistry.Events.DownloadFinished, this._onDownloadFinished.bind(this)),
     ];
@@ -91,6 +92,7 @@ class BrowserHandler {
     if (!this._shouldAttachToTarget(target))
       return;
     const session = this._dispatcher.createSession();
+    target.initSession(session);
     this._attachedSessions.set(target, session);
     this._session.emitEvent('Browser.attachedToTarget', {
       sessionId: session.sessionId(),
@@ -99,7 +101,11 @@ class BrowserHandler {
     sessions.push(session);
   }
 
-  async _onTargetDestroyed(target) {
+  _onTargetWillBeDestroyed({target, pendingActivity}) {
+    pendingActivity.push(this._detachFromTarget(target));
+  }
+
+  async _detachFromTarget(target) {
     const session = this._attachedSessions.get(target);
     if (!session)
       return;
diff --git a/browser_patches/firefox/juggler/protocol/Dispatcher.js b/browser_patches/firefox/juggler/protocol/Dispatcher.js
index c90903fcb4..242d7cb8a0 100644
--- a/browser_patches/firefox/juggler/protocol/Dispatcher.js
+++ b/browser_patches/firefox/juggler/protocol/Dispatcher.js
@@ -31,7 +31,7 @@ class Dispatcher {
 
   async destroySession(session) {
     this._sessions.delete(session.sessionId());
-    await session.dispose();
+    await session._dispose();
   }
 
   _dispose() {
@@ -108,7 +108,7 @@ class ProtocolSession {
     this._handlers.set(domainName, handler);
   }
 
-  async dispose() {
+  async _dispose() {
     const promises = [];
     for (const [domainName, handler] of this._handlers) {
       if (typeof handler.dispose !== 'function')