XHR timeout disabled is required for file uploads.

Herst · Herst · commit 81f5f9b05afb · 2015-06-01T15:26:20.000+02:00
A timeout (e.g. set globally to work around certain Google Chrome bugs) would otherwise break file uploads lasting longer than the set value.
diff --git a/js/jquery.fileupload.js b/js/jquery.fileupload.js
@@ -277,7 +277,8 @@
             // The following are jQuery ajax settings required for the file uploads:
             processData: false,
             contentType: false,
-            cache: false
+            cache: false,
+            timeout: 0
         },
 
         // A list of options that require reinitializing event listeners and/or
