diff --git a/Apps/Sandcastle/CesiumSandcastle.js b/Apps/Sandcastle/CesiumSandcastle.js
index b7f4163fe29a..ff9209cb0aca 100644
--- a/Apps/Sandcastle/CesiumSandcastle.js
+++ b/Apps/Sandcastle/CesiumSandcastle.js
@@ -618,7 +618,10 @@ require({
 
     // Apply user HTML to bucket.
     const htmlElement = bucketDoc.createElement("div");
-    htmlElement.innerHTML = htmlEditor.getValue();
+    // Stylesheet imports are weirdly broken in Firefox 140. This is a hacky workaround
+    // https://github.com/CesiumGS/cesium/issues/12700
+    const htmlCode = htmlEditor.getValue().replace(/@import/, "@import ");
+    htmlElement.innerHTML = htmlCode;
     bucketDoc.body.appendChild(htmlElement);
 
     const onScriptTagError = function () {
@@ -1176,7 +1179,9 @@ require({
     baseHref = `${baseHref.substring(0, pos)}/gallery/`;
 
     const code = jsEditor.getValue();
-    const html = htmlEditor.getValue();
+    // Stylesheet imports are weirdly broken in Firefox 140. This is a hacky workaround
+    // https://github.com/CesiumGS/cesium/issues/12700
+    const html = htmlEditor.getValue().replace(/@import/, "@import ");
     const data = makeCompressedBase64String([code, html, baseHref]);
 
     let url = getBaseUrl();