--- a/mobile/android/chrome/content/aboutDownloads.js
+++ b/mobile/android/chrome/content/aboutDownloads.js
@@ -325,17 +325,19 @@ DownloadItem.prototype = {
   get id() {
     return this._id;
   },
   get iconUrl() {
     return this._iconUrl;
   },
 
   get size() {
-    if (this.download.hasProgress) {
+    if (this.download.succeeded && this.download.target.exists) {
+      return DownloadUtils.convertByteUnits(this.download.target.size).join("");
+    } else if (this.download.hasProgress) {
       return DownloadUtils.convertByteUnits(this.download.totalBytes).join("");
     }
     return strings.GetStringFromName("downloadState.unknownSize");
   },
 
   get startDate() {
     return this._startDate;
   },