You mentioned: Searching through the jqXHR, you find the error: "Uploaded bytes exceed file size"

Maybe there is an issue with the computation of the file size, that somehow you get different results in Firefox than in the other browsers. Is that built-in to the function or does your code do the computation?

I got a little lost in the documentation here:

site:github.com/blueimp/jquery-file-upload "uploadedbytes" - Google Search

Thanks. In my estimation that is exactly the issue. But that doesn't help with a resolution.

The actual file size: 945,991 bytes

If Firefox is miscalculating the length (in Safari/Chrome 945991 and 946241 in Firefox), then Firefox is reporting erroneously and should be raised as a bug in Firefox, would you agree?

That seems like a big discrepancy. But I haven't looked in the script to see how it is computed. I suggest filing it as an issue with Blueimp to see whether they are aware of it and either have a solution or have filed a bug with Mozilla themselves.

Sorry, the length from Mozilla is: 946241. Still... it is way off.

I will do what you say re: posting this as an issue with Blueimp.

I have posted it here: https://groups.google.com/forum/#!topic/jquery-fileupload/8ufWGnX3MSA