Web Console

Watch the events occurring within your Web pages. Web Console lets you see logging messages from your JavaScript code, JavaScript and CSS errors and network activity. Search and filter to find just the events you need to look at. Plus, you can directly interact with and explore your page via JavaScript.

Page Inspector

Peek right into the styling of any Web page by visually selecting the page element that you’re interested in. Simply right-click on any part of the page and select “Inspect Element;” choose Inspect from the Web Developer menu; or use the handy ctrl-shift-I (cmd-shift-I on Mac) keyboard shortcut. (Try it out on this very page!)

Scratchpad

The browser is a fantastic place to experiment with JavaScript and Scratchpad lets you write code that can interact directly with the contents of a Web page. Scratchpad makes it easy to experiment with your ideas and then copy the results into your usual website development tools. It’s also fun for tinkering on top of pages.

Firebug

The Firebug add-on that web developers everywhere depend on is compatible with the latest version of Firefox.

More Development Resources

• Follow our development blog
• Follow our beta releases and tips blog
• Join a passionate community of developers learning and teaching through demos and documentation at developer.mozilla.org

Forms

Firefox implements HTML5 forms, and supports new input types, data list support, new input attributes like autofocus and placeholder, decoupled forms, form options, validation mechanisms, constraint validation and new CSS selectors to bind them all together. For more detailed information, visit our Hacks site.

Parser

Firefox includes an HTML5-ready parser which brings new capabilities like inline SVG, and also improves performance by running the parsing algorithm on its own processor. This brings the Firefox parser algorithm closer to the standard and lays the foundation for consistent parsing across browsers.

WebM

Firefox supports WebM, the new royalty-free format for video on the Web. It works on YouTube if you join their HTML5 beta, and works with embedded YouTube videos if you use their new br embedding API. Join the beta and see an example at the bottom of this post.

Video Buffer API

With support for the buffered attribute for HTML5 video, Web pages with video can now give an accurate measure of how much video has been buffered rather than an approximation based on the download rate and current position in the stream.

Video “Preload” Support

The “autobuffer" attribute for video has been replaced with the new “preload” attribute. This attribute gives developers control over how videos are pre-buffered if they’re included on a page rather than the binary on/off system that was included in Firefox 3.5.

History pushState and replaceState

Firefox supports the HTML5 pushState and replaceState history modification calls, allowing developers to create or modify the browser navigation history. These are helpful for applications that might want to generate history entries using the hash after the URL (useful for HTML-based slides, for example).

CSS Transitions

Firefox includes support for CSS transitions. Since the spec is still early, these are still –moz prefixed extensions.

CSS Animations

Firefox 5 supports CSS Animations: a way to define CSS keyframes to create complex animations.

-moz-calc()

Firefox supports an early version of calc that’s private-namespaced as –moz-calc. This allows developers to use simple expressions anywhere they can use a length, making CSS page layouts much simpler (no more divs for spacing!).

-moz-any()

Firefox has added an extremely useful new CSS extension: -moz-any() selector grouping. This allows providing alternatives between combinators rather than having to repeat the entire selector for one different piece.

-moz-element()

The –moz-element is an extension to the background-image property that lets you use any element as the background for another element.

-moz-placeholder

The :-moz-placeholder changes the attributes of the background text that’s a placeholder in an HTML5 form. Web developers can change the color or other attribute of the placeholder text.

Border Radius

The border-radius attribute is now supported, replacing the old -moz-border-radius version.

box-shadow

box-shadow has replaced -moz-box-shadow.

-moz-font-feature-settings

Firefox includes support for exposing much more of the capabilities of TrueType fonts with the -moz-font-feature-settings property. It’s possible to take advantage of all kinds of font capabilities — kerning, ligatures, alternates, real small caps and stylistic sets, to name just a few.

Consistent CSS Units

We’ve changed our handling of pixel sizes to match Internet Explorer, Safari and Chrome so that 1 inch always equals 96 pixels.

Physical CSS Unit Support

Firefox introduces a new CSS unit called mozmm for the rare instance where you actually want a physical size to be used.

device-pixel-ratio

The -moz-device-pixel-ratio media query gives you the number of device pixels per CSS pixel.

-moz-tab-size

The -moz-tab-size property lets you specify the width in space characters of how to render a tab character (U+0009) when rendering text.

-moz-focusring

Firefox’s CSS pseudo-selector, -moz-focusring, lets you specify the appearance of an element when it’s focused and when it would have a focus ring drawn around it. Different operating systems have different conventions for when to draw a focus ring or not, and this lets you control the look of form controls while maintaining platform conventions.

-moz-image-rect

The new -moz-image-rect lets you use a sub-rectangle of an image as part of a background or background-image.

Resizable Text Areas

Text areas are resizable by default. You can disable that with the new resize CSS property.

window.matchMedia

Firefox supports a JavaScript equivalent to CSS3 media queries, which allows Web pages to adapt to the media/device they are displayed on. Different information about the media is available, such as screen width, resolution and orientation.

WebSockets

Firefox supports a way to maintain two-way communications with a server. WebSockets make it possible to create real-time messaging applications and HTML5 games on the Web.

Server Sent Events

Server Sent Events enable a server to push messages to the browser, which can then be detected as events in the Web page.

ECMAScript 5

ECMAScript 5 is the new version of the JavaScript language, which includes new features and API like Strict Mode and the JSON API.

WebGL

Canvas 3D. WebGL brings 3D graphics to the Web by introducing an API that closely conforms to OpenGL ES 2.0 and can be used in HTML5 canvas elements.

Support for .click() to the File Upload Control

Firefox can call .click() on a hidden file control to bring up the platform file upload widget, meaning you can build your own instead of exposing the (ugly) file upload control. If you combine this with the new File APIs and progress events you’ll have a recipe for a very nice file upload experience.

Support for .slice in the File API

Firefox supports the Blob API and the .slice APIs that come with it. This can help people who want to process parts of large File objects from JavaScript without having to load the whole file into the memory. People who reliably upload large files can use some server and JS code to split a large file into sections and upload chunks, including re-retrying failed sections, or even uploading several sections, in parallel.

Support for File API URLs

Firefox supports the .url attribute for the File API, meaning objects from a File API can be used for images, video, HTML or other URL-powered objects.

Touch and Multi-Touch Events

Firefox supports both touch and multi-touch events, exposed to the DOM. Support for this functionality is available on Windows 7 systems.

Detect Click-to-Touch

Firefox can tell if a mouse or finger generated an event with the mozInputSource property. This is useful with the touch and multi-touch events and makes it possible to build apps that treat touch and mouse input differently.

IndexedDB

Firefox includes an early version of IndexedDB. This emerging standard for local storage is still undergoing change and will be private-prefixed until it’s stable. IndexedDB primer provides an overview of using the IndexedDB API.

FormData

Firefox includes support for the new FormData object, which makes it easier to interact with HTML forms. It also enables some new capabilities, like making it easy to upload a file as part of a form accessed via the File API.

Get a Canvas as a File Object

Firefox makes Canvas accessible as a file object for uploads and other purposes. You can now use the mozGetAsFile() method on a canvas and it will return an image file.

Audio Sampling and Generation API

The Firefox Audio Data API allows developers to read, modify and write data from audio and video elements.

SVG Animation and SMIL

Now you can animate SVG with SMIL in Firefox.

SVG As Images and CSS Backgrounds

SVG can now be used in <img> tags as well as background images in CSS. SMIL animations are also supported.

Content Security Policy

Content Security Policy (CSP) is a set of tools developers can use to help prevent a few different classes of attacks. In particular, it offers tools to mitigate cross-site scripting attacks, click-jacking and packet sniffing attacks. When a rule is violated, Firefox can send back information about that violation to the website, helping improve security for other browsers too.

X-Frame-Options

Firefox supports the X-Frame-Options header, one defense against clickjacking. This response header is supported by other browsers as well.

HSTS (ForceHTTPS)

Firefox supports the HTTP Strict Transport Security (HSTS) headers. These headers can be used to tell the browser that it should never, ever contact a site over unencrypted HTTP.

CORS Improvements

Firefox fixes bugs in the CORS implementation.

:visited changes

Firefox includes the changes required to help improve your privacy online by closing a decade-old hole in CSS rules that let any website query your browsing history. These changes have also been picked up by WebKit-based browsers.