Current versions of Firefox, Chrome, and Safari support at least a portion of the HTML 5 File API. Among other things, this allows getting at metadata about files that have been selected in an <input type="file"> widget such as the file size and type.
Type information isn't entirely reliable as type detection & extension maps may vary between client and server, but size should be pretty good!
This will allow us to check the file size on selection and tell the user that it ain't gonna fit in our upload size limits before they submit the form.
http://hacks.mozilla.org/2009/12/w3c-fileapi-in-firefox-3-6/
Version: 1.17.x
Severity: enhancement