W3C FileAPI in Firefox 3.6 at hacks.mozilla.org

"Often, web applications will prompt the user to select a file, typically to upload to a server. Unless the web application makes use of a plugin, file selection occurs through an HTML input element, of the sort . Firefox 3.6 now supports much of the W3C File API, which specifies the ability to asynchronously read the selected file into memory, and perform operations on the file data within the web application (for example, to display a thumbnail preview of an image, before it is uploaded, or to look for ID3 tags within an MP3 file, or to look for EXIF data in JPEG files, all on the client side). This is a new API, and replaces the file API that was introduced in Firefox 3."