HiDPI support, HTML5 notifications, Parallel JS, asm.js and more – Firefox Development Highlights

Time for another look at the latest developments with Firefox. This is part of our Bleeding Edge and Firefox Development Highlights series, and most examples only work in Firefox Nightly (and could be subject to change).

HiDPI support

We’re happy to say that ico/icns with multiple images are now supported: the highest resolution icon is now used on HiDPI/Retina displays.

Favicon implementation is described in bug 828508 and ico/icns is described in bug 419588.

Performance improvements/Snappy:

Numerous performance improvements have been made, such as faster startup, better scrolling on touchpads and smoother animations.

The most important improvement, however, is probably multithreaded image decoder. The result should be faster page loads and tab switching. All the nitty-gritty detalis are described in bug 716140.


When it comes to the world of HTML5 & friends, we have some good additional support:

<input type=”range”>

We now support the <input type="range"> element in forms. To style it, you can use the ::-moz-range-progress:

::-moz-range-progress {
    background: #f00;
<input type="range">

You can see this <input type=”range”> demo in action on jsFiddle.

HTML5 notifications

HTML5 notifications have now been implemented. Basically, you ask for permission and then you can create a notification:

function authorizeNotification() {
    Notification.requestPermission(function(perm) {
function showNotification() {
    var notification = new Notification("This is a title", {
        dir: "auto",
        lang: "",
        body: "This is a notification body",
        tag: "sometag",

See the HTML5 notification demo in action on jsFiddle.

WebAudio API activated by default

WebAudio API has been activated by default in Firefox Nightly. Testers welcome, though there are still work to be done before it can be released.


Parallel JS

The first version of Parallel JS has landed for Firefox. A lot more details in the Parallel JS Lands article.


We’re happy to say that asm.js is now in Firefox, scheduled to be released in Firefox 22! Luke Wagner has written more about it in asm.js in Firefox Nightly.

ES6 Arrow function syntax

We now support the ES6 Arrow function syntax

let square = x => x*x;


@supports activated by default

We plan on releasing this with Firefox 22. More about @supports on MDN.

min-width and min-height ‘auto’ keyword

min-width and min-height 'auto' keyword is no more supported. It has been removed from CSS3 Flexbox. More about that in bug 848539.

CSS Flexbox has been re-enabled

Happy to let you know that CSS Flexbox has been re-enabled by default in Firefox 22, which is currently in Firefox Aurora!

View full post on Mozilla Hacks – the Web developer blog

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