Bug 2074956 / Demo

Public test case for Mozilla bug 2074956: HTTP/3: POST response discarded with NS_ERROR_NET_RESET

What this page does

A plain WordPress install with one tiny plugin. Each button sends a request to admin-ajax.php, which answers with the current server time as JSON or with a 302 redirect. No login, no cookies, no other plugins.

Steps to reproduce

  1. Open this page in Firefox 156 or later with HTTP/3 enabled (the default).
  2. Check that the page was loaded via h3 (shown below). Reload if it says h2.
  3. Click the POST buttons, several times each.
Expected
HTTP 200 with the server time, as over HTTP/2 or in other browsers.
Actual
The POST fails with NS_ERROR_NET_RESET (logged here as a network error), although the server has processed the request. The redirect is never followed.
Workaround
Set network.http.http3.enable to false in about:config.

Test

Target
https://bug.gregermax.media/wp-admin/admin-ajax.php
Browser
Page loaded via ?. The bug only occurs over h3; reload once or twice if this shows h2.