diff --git a/browser_patches/firefox-beta/BUILD_NUMBER b/browser_patches/firefox-beta/BUILD_NUMBER
index 8a4fc24cd1..d30fa46dce 100644
--- a/browser_patches/firefox-beta/BUILD_NUMBER
+++ b/browser_patches/firefox-beta/BUILD_NUMBER
@@ -1,2 +1,2 @@
-1265
-Changed: max@schmitt.mx Mon Jun 28 22:40:00 UTC 2021
+1266
+Changed: max@schmitt.mx Tue Jun 29 22:44:52 UTC 2021
diff --git a/browser_patches/firefox-beta/juggler/TargetRegistry.js b/browser_patches/firefox-beta/juggler/TargetRegistry.js
index 608a3f3d4f..29f34cc679 100644
--- a/browser_patches/firefox-beta/juggler/TargetRegistry.js
+++ b/browser_patches/firefox-beta/juggler/TargetRegistry.js
@@ -12,6 +12,8 @@ const {NetUtil} = ChromeUtils.import('resource://gre/modules/NetUtil.jsm');
 const {AppConstants} = ChromeUtils.import("resource://gre/modules/AppConstants.jsm");
 const {OS} = ChromeUtils.import("resource://gre/modules/osfile.jsm");
 
+const Cr = Components.results;
+
 const helper = new Helper();
 
 const IDENTITY_NAME = 'JUGGLER ';
@@ -26,6 +28,7 @@ class DownloadInterceptor {
   constructor(registry) {
     this._registry = registry
     this._handlerToUuid = new Map();
+    this._uuidToHandler = new Map();
   }
 
   //
@@ -60,6 +63,7 @@ class DownloadInterceptor {
     }
     outFile.value = file;
     this._handlerToUuid.set(externalAppHandler, uuid);
+    this._uuidToHandler.set(uuid, externalAppHandler);
     const downloadInfo = {
       uuid,
       browserContextId: browserContext.browserContextId,
@@ -76,16 +80,24 @@ class DownloadInterceptor {
     if (!uuid)
       return;
     this._handlerToUuid.delete(externalAppHandler);
+    this._uuidToHandler.delete(uuid);
     const downloadInfo = {
       uuid,
+      error: errorName,
     };
-    if (errorName === 'NS_BINDING_ABORTED') {
+    if (canceled === 'NS_BINDING_ABORTED') {
       downloadInfo.canceled = true;
-    } else {
-      downloadInfo.error = errorName;
     }
     this._registry.emit(TargetRegistry.Events.DownloadFinished, downloadInfo);
   }
+
+  async cancelDownload(uuid) {
+    const externalAppHandler = this._uuidToHandler.get(uuid);
+    if (!externalAppHandler) {
+      return;
+    }
+    await externalAppHandler.cancel(Cr.NS_BINDING_ABORTED);
+  }
 }
 
 const screencastService = Cc['@mozilla.org/juggler/screencast;1'].getService(Ci.nsIScreencastService);
@@ -227,13 +239,18 @@ class TargetRegistry {
     };
 
     const extHelperAppSvc = Cc["@mozilla.org/uriloader/external-helper-app-service;1"].getService(Ci.nsIExternalHelperAppService);
-    extHelperAppSvc.setDownloadInterceptor(new DownloadInterceptor(this));
+    this._downloadInterceptor = new DownloadInterceptor(this);
+    extHelperAppSvc.setDownloadInterceptor(this._downloadInterceptor);
 
     Services.wm.addListener({ onOpenWindow, onCloseWindow });
     for (const win of Services.wm.getEnumerator(null))
       onOpenWindow(win);
   }
 
+  async cancelDownload(options) {
+    this._downloadInterceptor.cancelDownload(options.uuid);
+  }
+
   setBrowserProxy(proxy) {
     this._browserProxy = proxy;
   }
diff --git a/browser_patches/firefox-beta/juggler/protocol/BrowserHandler.js b/browser_patches/firefox-beta/juggler/protocol/BrowserHandler.js
index 642281b688..a6c7449f46 100644
--- a/browser_patches/firefox-beta/juggler/protocol/BrowserHandler.js
+++ b/browser_patches/firefox-beta/juggler/protocol/BrowserHandler.js
@@ -125,6 +125,10 @@ class BrowserHandler {
     this._session.emitEvent('Browser.downloadFinished', downloadInfo);
   }
 
+  async ['Browser.cancelDownload']({uuid}) {
+    await this._targetRegistry.cancelDownload({uuid});
+  }
+
   async ['Browser.newPage']({browserContextId}) {
     const targetId = await this._targetRegistry.newPage({browserContextId});
     return {targetId};
diff --git a/browser_patches/firefox-beta/juggler/protocol/Protocol.js b/browser_patches/firefox-beta/juggler/protocol/Protocol.js
index f658c5082f..d179f93cd4 100644
--- a/browser_patches/firefox-beta/juggler/protocol/Protocol.js
+++ b/browser_patches/firefox-beta/juggler/protocol/Protocol.js
@@ -452,6 +452,11 @@ const Browser = {
         height: t.Number,
       },
     },
+    'cancelDownload': {
+      params: {
+        uuid: t.Optional(t.String),
+      }
+    }
   },
 };
 
diff --git a/browser_patches/firefox/BUILD_NUMBER b/browser_patches/firefox/BUILD_NUMBER
index 0a84548b73..c909c0b8f3 100644
--- a/browser_patches/firefox/BUILD_NUMBER
+++ b/browser_patches/firefox/BUILD_NUMBER
@@ -1,2 +1,2 @@
-1272
-Changed: max@schmitt.mx Mon Jun 28 10:29:55 UTC 2021
+1273
+Changed: max@schmitt.mx Tue Jun 29 22:39:37 UTC 2021
diff --git a/browser_patches/firefox/juggler/TargetRegistry.js b/browser_patches/firefox/juggler/TargetRegistry.js
index 608a3f3d4f..29f34cc679 100644
--- a/browser_patches/firefox/juggler/TargetRegistry.js
+++ b/browser_patches/firefox/juggler/TargetRegistry.js
@@ -12,6 +12,8 @@ const {NetUtil} = ChromeUtils.import('resource://gre/modules/NetUtil.jsm');
 const {AppConstants} = ChromeUtils.import("resource://gre/modules/AppConstants.jsm");
 const {OS} = ChromeUtils.import("resource://gre/modules/osfile.jsm");
 
+const Cr = Components.results;
+
 const helper = new Helper();
 
 const IDENTITY_NAME = 'JUGGLER ';
@@ -26,6 +28,7 @@ class DownloadInterceptor {
   constructor(registry) {
     this._registry = registry
     this._handlerToUuid = new Map();
+    this._uuidToHandler = new Map();
   }
 
   //
@@ -60,6 +63,7 @@ class DownloadInterceptor {
     }
     outFile.value = file;
     this._handlerToUuid.set(externalAppHandler, uuid);
+    this._uuidToHandler.set(uuid, externalAppHandler);
     const downloadInfo = {
       uuid,
       browserContextId: browserContext.browserContextId,
@@ -76,16 +80,24 @@ class DownloadInterceptor {
     if (!uuid)
       return;
     this._handlerToUuid.delete(externalAppHandler);
+    this._uuidToHandler.delete(uuid);
     const downloadInfo = {
       uuid,
+      error: errorName,
     };
-    if (errorName === 'NS_BINDING_ABORTED') {
+    if (canceled === 'NS_BINDING_ABORTED') {
       downloadInfo.canceled = true;
-    } else {
-      downloadInfo.error = errorName;
     }
     this._registry.emit(TargetRegistry.Events.DownloadFinished, downloadInfo);
   }
+
+  async cancelDownload(uuid) {
+    const externalAppHandler = this._uuidToHandler.get(uuid);
+    if (!externalAppHandler) {
+      return;
+    }
+    await externalAppHandler.cancel(Cr.NS_BINDING_ABORTED);
+  }
 }
 
 const screencastService = Cc['@mozilla.org/juggler/screencast;1'].getService(Ci.nsIScreencastService);
@@ -227,13 +239,18 @@ class TargetRegistry {
     };
 
     const extHelperAppSvc = Cc["@mozilla.org/uriloader/external-helper-app-service;1"].getService(Ci.nsIExternalHelperAppService);
-    extHelperAppSvc.setDownloadInterceptor(new DownloadInterceptor(this));
+    this._downloadInterceptor = new DownloadInterceptor(this);
+    extHelperAppSvc.setDownloadInterceptor(this._downloadInterceptor);
 
     Services.wm.addListener({ onOpenWindow, onCloseWindow });
     for (const win of Services.wm.getEnumerator(null))
       onOpenWindow(win);
   }
 
+  async cancelDownload(options) {
+    this._downloadInterceptor.cancelDownload(options.uuid);
+  }
+
   setBrowserProxy(proxy) {
     this._browserProxy = proxy;
   }
diff --git a/browser_patches/firefox/juggler/protocol/BrowserHandler.js b/browser_patches/firefox/juggler/protocol/BrowserHandler.js
index 642281b688..a6c7449f46 100644
--- a/browser_patches/firefox/juggler/protocol/BrowserHandler.js
+++ b/browser_patches/firefox/juggler/protocol/BrowserHandler.js
@@ -125,6 +125,10 @@ class BrowserHandler {
     this._session.emitEvent('Browser.downloadFinished', downloadInfo);
   }
 
+  async ['Browser.cancelDownload']({uuid}) {
+    await this._targetRegistry.cancelDownload({uuid});
+  }
+
   async ['Browser.newPage']({browserContextId}) {
     const targetId = await this._targetRegistry.newPage({browserContextId});
     return {targetId};
diff --git a/browser_patches/firefox/juggler/protocol/Protocol.js b/browser_patches/firefox/juggler/protocol/Protocol.js
index f658c5082f..d179f93cd4 100644
--- a/browser_patches/firefox/juggler/protocol/Protocol.js
+++ b/browser_patches/firefox/juggler/protocol/Protocol.js
@@ -452,6 +452,11 @@ const Browser = {
         height: t.Number,
       },
     },
+    'cancelDownload': {
+      params: {
+        uuid: t.Optional(t.String),
+      }
+    }
   },
 };