部署在Heroku的应用在Firefox中遇script标签后停止渲染求助

我的应用部署到Heroku后，Firefox浏览器在加载到某一特定script标签时就停止页面渲染，但相同应用在本地部署时运行完全正常。以下是出现该问题的Heroku站点链接（截至撰稿时仍存在故障）：
https://idom-docs.herokuapp.com

经检查控制台无特殊报错，页面仅在遇到该script标签后直接停止渲染。

以下是问题演示GIF：左侧为Chromium内核浏览器，右侧为Firefox。可见Chromium可正常滚动浏览全部示例，而Firefox即便所有资源都已加载完成，也仅能渲染第一个示例，之后页面停留在加载状态。但切换到本地部署的站点时，Firefox可正常完成全页渲染。

相关script代码示例如下：

<script async type="module">
    import {{ mountWidgetExample }} from "/_static/custom.js";
    mountWidgetExample("some-element-id", "some-uuid", "/_host");
</script>

custom.js内容如下：

import { mountLayoutWithWebSocket } from "idom-client-react";

const LOC = window.location;
const HTTP_PROTO = LOC.protocol;
const WS_PROTO = HTTP_PROTO === "https:" ? "wss:" : "ws:";
const IDOM_MODULES_PATH = "/_modules";

export function mountWidgetExample(mountID, viewID, idomServerHost) {
  const idom_url = "//" + (idomServerHost || LOC.host);
  const http_idom_url = HTTP_PROTO + idom_url;
  const ws_idom_url = WS_PROTO + idom_url;

  const mountEl = document.getElementById(mountID);
  const enableWidgetButton = document.createElement("button");
  enableWidgetButton.appendChild(document.createTextNode("Enable Widget"));
  enableWidgetButton.setAttribute("class", "enable-widget-button");

  enableWidgetButton.addEventListener("click", () =>
    fadeOutElementThenCallback(enableWidgetButton, () => {
      {
        mountEl.removeChild(enableWidgetButton);
        mountEl.setAttribute("class", "interactive widget-container");
        mountLayoutWithWebSocket(
          mountEl,
          ws_idom_url + `/_idom/stream?view_id=${viewID}`,
          (source, sourceType) =>
            loadImportSource(http_idom_url, source, sourceType)
        );
      }
    })
  );

  function fadeOutElementThenCallback(element, callback) {
    {
      var op = 1; // initial opacity
      var timer = setInterval(function () {
        {
          if (op < 0.001) {
            {
              clearInterval(timer);
              element.style.display = "none";
              callback();
            }
          }
          element.style.opacity = op;
          element.style.filter = "alpha(opacity=" + op * 100 + ")";
          op -= op * 0.5;
        }
      }, 50);
    }
  }

  mountEl.appendChild(enableWidgetButton);
}

function loadImportSource(baseUrl, source, sourceType) {
  if (sourceType == "NAME") {
    return import(baseUrl + IDOM_MODULES_PATH + "/" + source);
  } else {
    return import(source);
  }
}

内容的提问来源于stack exchange，提问作者rmorshea