Apache commons fileupload timeout only with Firefox

A few things that are worth to try here:

• Explicit the encoding: https://stackoverflow.com/a/10488411/4279120
• Decompose your call and add iteration and try catch, ex. : https://www.programcreek.com/java-api-examples/?api=org.apache.commons.fileupload.FileItemIterator
• Take a look at the MultipartConfig, it seems to provide such attributes as maxFileSize and maxRequestSize (see: https://www.codejava.net/java-ee/servlet/java-file-upload-example-with-servlet-30-api#maxFileSize%28%29)
• Manually define the header of your Request if you can. It seems that adding "X-File-Name" and "X-File-Size", can also help, but this is a little old: AJAX File Upload with XMLHttpRequest

We may also help you better if you provide some more informations, like the versions of apache / java / servlet, and a few more code (especially the definition of request)

Some ressources that could be helpful:
XMLHttpRequest
Sending_files_using_a_FormData_object
How to set a header for a HTTP GET request, and trigger file download?

You can try setting the maximum file size, maybe the file size exceeds the maximum threshold .According to the documentation :

• Uploaded items should be retained in memory as long as they are reasonably small.
• Larger items should be written to a temporary file on disk.
• Very large upload requests should not be permitted.
• The built-in defaults for the maximum size of an item to be retained in memory, the maximum permitted size of an upload request, and the location of temporary files are acceptable.

Try the following :

 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        try {
            // Set factory constraints
           DiskFileItemFactory factory = new DiskFileItemFactory();
           factory.setSizeThreshold(yourMaxMemorySize);
           ServletContext servletContext = this.getServletConfig().getServletContext();
           File repository = (File) servletContext.getAttribute("javax.servlet.context.tempdir");
           factory.setRepository(repository);
            List<FileItem> items = new ServletFileUpload(factory).parseRequest(request);
            for (FileItem item : items) {
                if (item.isFormField()) {
                    // Process regular form field (input type="text|radio|checkbox|etc", select, etc).
                    String fieldName = item.getFieldName();
                    String fieldValue = item.getString();
                    // ... (do your job here)
                } else {
                    // Process form file field (input type="file").
                    String fieldName = item.getFieldName();
                    String fileName = FilenameUtils.getName(item.getName());
                    InputStream fileContent = item.getInputStream();
                    // ... (do your job here)
                }
            }
        } catch (FileUploadException e) {
            throw new ServletException("Cannot parse multipart request.", e);
        }

        // ...
    }

Here, we are providing a temp location for the file since the file is large.