diff --git a/packages/playwright-core/browsers.json b/packages/playwright-core/browsers.json
index d6d6e27db6..2a453116f4 100644
--- a/packages/playwright-core/browsers.json
+++ b/packages/playwright-core/browsers.json
@@ -13,7 +13,7 @@
     },
     {
       "name": "firefox",
-      "revision": "1311",
+      "revision": "1312",
       "installByDefault": true
     },
     {
diff --git a/packages/playwright-core/src/server/firefox/ffNetworkManager.ts b/packages/playwright-core/src/server/firefox/ffNetworkManager.ts
index d2bac24fef..56893dd3ed 100644
--- a/packages/playwright-core/src/server/firefox/ffNetworkManager.ts
+++ b/packages/playwright-core/src/server/firefox/ffNetworkManager.ts
@@ -131,7 +131,8 @@ export class FFNetworkManager {
       this._requests.delete(request._id);
       response._requestFinished(responseEndTime);
     }
-    response._setHttpVersion(event.protocolVersion);
+    if (event.protocolVersion)
+      response._setHttpVersion(event.protocolVersion);
     this._page._frameManager.reportRequestFinished(request.request, response);
   }
 
diff --git a/packages/playwright-core/src/server/firefox/protocol.d.ts b/packages/playwright-core/src/server/firefox/protocol.d.ts
index 7f34b1558d..00e7649417 100644
--- a/packages/playwright-core/src/server/firefox/protocol.d.ts
+++ b/packages/playwright-core/src/server/firefox/protocol.d.ts
@@ -901,7 +901,7 @@ export module Protocol {
       responseEndTime: number;
       transferSize: number;
       encodedBodySize: number;
-      protocolVersion: string;
+      protocolVersion?: string;
     }
     export type requestFailedPayload = {
       requestId: string;