Is there a buffer limit (file size or number) in modern browsers that have implemented FormData and XmlHttpRequest?

I am introducing XmlHttpRequest and FormData for a new application on our website, and there is a concern that some clients may try to load tens or maybe hundreds of thousands of documents at a time. Before I began to painstakingly test these conditions, I was hoping that someone would know if there is a limit on (1) the number of files that can be downloaded at a time, and / or (2) if there is a file size limit in any of the modern browsers that have implemented these features.