diff --git a/packages/trace-viewer/src/ui/uiModeTraceView.tsx b/packages/trace-viewer/src/ui/uiModeTraceView.tsx
index 2f52467fc8..71f9e2e23c 100644
--- a/packages/trace-viewer/src/ui/uiModeTraceView.tsx
+++ b/packages/trace-viewer/src/ui/uiModeTraceView.tsx
@@ -118,6 +118,7 @@ async function loadSingleTraceFile(traceURL: URL): Promise<MultiTraceModel> {
 }
 
 function formatUrl(traceURL: URL) {
+  // Dropbox does not support cors.
   if (traceURL.hostname === 'dropbox.com')
     traceURL.hostname = 'dl.dropboxusercontent.com';