Is mozFullPath in Firefox a security risk during file upload?

Question

I am working on a small photo application in which the user selects a local file and it is placed on the canvas using window.URL.createObjectURL(file) - really the main material. During testing, I briefly dumped the contents of the file array onto the console - just to make sure that I get what I want.

I am using Firefox 31.0 (not Iceweasel) and Chrome 34.0.1847.116 (not Chromium) on Debian 7

I call the array as follows:

  var file = evnt.target.files[0]; if (file) { console.log('file'); // other stuff } 

The .log console looks like this in a Google Chrome browser:

 File { name: "image.png" size: 55464 type: "image/png" webkitRelativePath: "" } 

And as in the Mozilla Firefox browser:

 File { size: 55464, type: "image/png", name: "image.png", path: "", lastModifiedDate: Date 2014-09-09T13:30:30.000Z, mozFullPath: "/home/server/Desktop/image.png" } 

I can request:

 console.log(evnt.target.files[0]['type') 

and correctly get "image/png" as the answer, however, when I ask:

 console.log(evnt.target.files[0]['mozFullPath']); 

I just get the answer: ""

Why does this information flow through the evnt.target.files[0] array, but is invisible when I call it directly?

Is this information about the structure of my file system only displayed by my privileged console, or can it be passed through man-in-the-middle attacks in my browser?

EDIT

In older Firefox browsers, this would improve permissions:

 netscape.security.PrivilegeManager.enablePrivilege("UniversalBrowserRead"); 

But this is no more. Anyway, this is a problem when using Firefox on public Linux terminals / other people's computers, because it is leaking file system data, such as the directory structure and system username. Together with other feats, this seems to me a dangerous threat ... Or am I just overreacting?