Building a Better Photo Uploader – Facebook

With these goals in mind we considered some of the existing options out there — Adobe Flash, Google Gears, Yahoo! Browser Plus — but none of them carried the specific functionality we needed. This brought on an interesting challenge: We’d build a headless browser plug-in that could securely provide powerful JavaScript APIs — like filesystem browsing, background uploading threads, and thumbnailing — to our front-end code. With this system we are able to build the uploader’s UI entirely in HTML and CSS, where iteration is cheap and easy.
(Link: Building a Better Photo Uploader – Facebook)