Firefox Nightly
Release Notes

Starting with Firefox 129, Firefox Nightly will automatically try to use a secure HTTPS connection whenever possible when loading a page. This behavior is known as "HTTPS-First", or "HTTPS Upgrades", and has been the default in Firefox's private browsing mode since Firefox 91. Here is a blog post from when this feature was introduced in Private Browsing.

Firefox now blocks third-party cookie access with Enhanced Tracking Protection's Strict mode.

WebRender hardware accelerated rendering is now enabled for most SVG Filter Primitives, improving performance of certain graphics-heavy content. Accelerated filters are feBlend, feColorMatrix, feComponentTransfer, feComposite, feDropShadow, feFlood, feGaussianBlur, feMerge and feOffset.

If we have the server time, we adjust the "expire" attribute value by adding the delta between the server and the local times. If the current time is set in the future, we consider valid cookies that are not expired for the server.

Starting with Firefox for Android 131, HLS playlist support was deprecated in Nightly builds. Extended testing showed no adverse impact as newer playback technologies have been widely adopted by websites.

As a follow-up to our work to upgrade mixed content starting Firefox 127, we will now also block HTTP-favicons if they can not be received over HTTPS instead.

Firefox for Android now uses resizes-visual as the default value of the interactive-widget property of the viewport <meta> element. This means that when the software keyboard is shown, Firefox resizes the page's visual viewport but not its layout viewport, avoiding an expensive reflow and resulting in a more usable layout on many pages.

Support for HTTP/2 Push has been removed due to compatibility issues with various sites. This feature is not currently supported by any other major browser.

Starting with Firefox Nightly 131, support for the non-mandatory options argument to getBBox will get the bounding box of the element, including its stroke (e.g. element.getBBox({"stroke": true})). (Learn more)

The requestVideoFrameCallback() method is now available on the HTMLVideoElement interface. This method enables developers to perform efficient operations on each video frame.

Added support for a post-quantum key exchange mechanism for TLS 1.3 (mlkem768x25519).

The getCapabilities method allows applications to gather the media capabilities supported for the live MediaStreamTrack.

The fetchpriority attribute enables web developers to optimize resource loading by specifying the relative priority of resources to be fetched by the browser. It accepts three values: auto (default priority), low (lower priority), high (higher priority). It can be specified on script, link, img elements, on the RequestInit parameter of the fetch() method and Link response headers. The HTML specification leaves the detailed interpretation of this attribute up to implementers. Firefox will typically use it to increase or decrease the urgency parameter of HTTP/2 and HTTP/3 requests.