I just committed my work in Bug 676619, which allows you to use the download attribute with <a> and <area>. This feature was previously implemented in WebKit. It allows you to easily offer files as downloads. I am mostly excited about the possible interactions with Blobs.
var blob = new Blob(["Hello World"]);
var a = document.createElement("a");
a.href = window.URL.createObjectURL(blob);
a.download = "hello-world.txt";
a.textContent = "Download Hello World!";