--- a/mail/components/downloads/content/aboutDownloads.js
+++ b/mail/components/downloads/content/aboutDownloads.js
@@ -104,21 +104,21 @@ var DownloadsView = {
 
   clearDownloads() {
     Downloads.getList(Downloads.ALL)
              .then(list => list.removeFinished())
              .then(null, Cu.reportError);
   },
 
   searchDownloads() {
-    let searchString = document.getElementById("searchBox").value;
+    let searchString = document.getElementById("searchBox").value.toLowerCase();
     for (let i = 0; i < this.listElement.itemCount; i++) {
       let downloadElem = this.listElement.getItemAtIndex(i);
       downloadElem.collapsed =
-        !downloadElem.downloadItem.fileName.includes(searchString);
+        !downloadElem.downloadItem.fileName.toLowerCase().includes(searchString);
     }
     this.listElement.clearSelection();
   },
 
   supportsCommand(aCommand) {
     return (this.commands.includes(aCommand) ||
             (DownloadItem.prototype.supportsCommand(aCommand)));
   },