1 files changed, 13 insertions, 1 deletions
diff --git a/browser/components/messagepreview/messagepreview.js b/browser/components/messagepreview/messagepreview.js
index 48e5fb1ff5..bec0a2d8eb 100644
--- a/browser/components/messagepreview/messagepreview.js
+++ b/browser/components/messagepreview/messagepreview.js
@@ -6,13 +6,25 @@
 
 "use strict";
 
+// decode a 16-bit string in which only one byte of each
+// 16-bit unit is occupied, to UTF-8. This is necessary to
+// comply with `btoa` API constraints.
+function fromBinary(encoded) {
+  const binary = atob(decodeURIComponent(encoded));
+  const bytes = new Uint8Array(binary.length);
+  for (let i = 0; i < bytes.length; i++) {
+    bytes[i] = binary.charCodeAt(i);
+  }
+  return String.fromCharCode(...new Uint16Array(bytes.buffer));
+}
+
 function decodeMessageFromUrl() {
   const url = new URL(document.location.href);
 
   if (url.searchParams.has("json")) {
     const encodedMessage = url.searchParams.get("json");
 
-    return atob(encodedMessage);
+    return fromBinary(encodedMessage);
   }
   return null;
 }