diff --git a/browser_patches/firefox-beta/BUILD_NUMBER b/browser_patches/firefox-beta/BUILD_NUMBER
index 5d63b9cc79..0bbe571ee7 100644
--- a/browser_patches/firefox-beta/BUILD_NUMBER
+++ b/browser_patches/firefox-beta/BUILD_NUMBER
@@ -1,2 +1,2 @@
-1311
-Changed: lushnikov@chromium.org Tue Dec 14 23:27:53 PST 2021
+1312
+Changed: lushnikov@chromium.org Tue Dec 28 13:12:02 MST 2021
diff --git a/browser_patches/firefox-beta/juggler/NetworkObserver.js b/browser_patches/firefox-beta/juggler/NetworkObserver.js
index 10ecca520b..2cbe92dc38 100644
--- a/browser_patches/firefox-beta/juggler/NetworkObserver.js
+++ b/browser_patches/firefox-beta/juggler/NetworkObserver.js
@@ -554,12 +554,18 @@ class NetworkRequest {
   _sendOnRequestFinished() {
     const pageNetwork = this._pageNetwork;
     if (pageNetwork) {
+      let protocolVersion = undefined;
+      try {
+        protocolVersion = this.httpChannel.protocolVersion;
+      } catch (e) {
+        // protocolVersion is unavailable in certain cases.
+      };
       pageNetwork.emit(PageNetwork.Events.RequestFinished, {
         requestId: this.requestId,
         responseEndTime: this.httpChannel.responseEndTime,
         transferSize: this.httpChannel.transferSize,
         encodedBodySize: this.httpChannel.encodedBodySize,
-        protocolVersion: this.httpChannel.protocolVersion,
+        protocolVersion,
       }, this._frameId);
     }
     this._networkObserver._channelToRequest.delete(this.httpChannel);
diff --git a/browser_patches/firefox-beta/juggler/protocol/Protocol.js b/browser_patches/firefox-beta/juggler/protocol/Protocol.js
index f2f99bc0b2..714b4fbda9 100644
--- a/browser_patches/firefox-beta/juggler/protocol/Protocol.js
+++ b/browser_patches/firefox-beta/juggler/protocol/Protocol.js
@@ -503,7 +503,7 @@ const Network = {
       responseEndTime: t.Number,
       transferSize: t.Number,
       encodedBodySize: t.Number,
-      protocolVersion: t.String,
+      protocolVersion: t.Optional(t.String),
     },
     'requestFailed': {
       requestId: t.String,
diff --git a/browser_patches/firefox/BUILD_NUMBER b/browser_patches/firefox/BUILD_NUMBER
index 4000f7197a..0bbe571ee7 100644
--- a/browser_patches/firefox/BUILD_NUMBER
+++ b/browser_patches/firefox/BUILD_NUMBER
@@ -1,2 +1,2 @@
-1311
-Changed: lushnikov@chromium.org Tue Dec 14 23:26:10 PST 2021
+1312
+Changed: lushnikov@chromium.org Tue Dec 28 13:12:02 MST 2021
diff --git a/browser_patches/firefox/juggler/NetworkObserver.js b/browser_patches/firefox/juggler/NetworkObserver.js
index 10ecca520b..2cbe92dc38 100644
--- a/browser_patches/firefox/juggler/NetworkObserver.js
+++ b/browser_patches/firefox/juggler/NetworkObserver.js
@@ -554,12 +554,18 @@ class NetworkRequest {
   _sendOnRequestFinished() {
     const pageNetwork = this._pageNetwork;
     if (pageNetwork) {
+      let protocolVersion = undefined;
+      try {
+        protocolVersion = this.httpChannel.protocolVersion;
+      } catch (e) {
+        // protocolVersion is unavailable in certain cases.
+      };
       pageNetwork.emit(PageNetwork.Events.RequestFinished, {
         requestId: this.requestId,
         responseEndTime: this.httpChannel.responseEndTime,
         transferSize: this.httpChannel.transferSize,
         encodedBodySize: this.httpChannel.encodedBodySize,
-        protocolVersion: this.httpChannel.protocolVersion,
+        protocolVersion,
       }, this._frameId);
     }
     this._networkObserver._channelToRequest.delete(this.httpChannel);
diff --git a/browser_patches/firefox/juggler/protocol/Protocol.js b/browser_patches/firefox/juggler/protocol/Protocol.js
index f2f99bc0b2..714b4fbda9 100644
--- a/browser_patches/firefox/juggler/protocol/Protocol.js
+++ b/browser_patches/firefox/juggler/protocol/Protocol.js
@@ -503,7 +503,7 @@ const Network = {
       responseEndTime: t.Number,
       transferSize: t.Number,
       encodedBodySize: t.Number,
-      protocolVersion: t.String,
+      protocolVersion: t.Optional(t.String),
     },
     'requestFailed': {
       requestId: t.String,