📃 June 2021 release notes

Widely available

The following features are now widely available:

Constraint validation API: Methods that validate form controls before submission, such as checkValidity(), reportValidity() and setCustomValidity().
Interaction media queries: The pointer, any-pointer, hover, and any-hover CSS media queries set styles based on the presence of pointing devices and their ability to hover over elements. For example, most smartphones match the (hover: none) and (pointer: coarse) media query.

New in Firefox

The following features are now available in Firefox:

aspect-ratio: The aspect-ratio CSS property controls the width-to-height ratio of elements. For <img> and <video> elements, the width and height attributes used together with height: auto control the aspect ratio while the image/video is loading.
Event timing: The event and first-input performance entries and the PerformanceEventTiming API measures the latency of user input events, such as mouse clicks or keypresses, and the latency of the first user input. First Input Delay (FID) is a common metric for perceived responsiveness.
Font metric overrides: The ascent-override, descent-override, and line-gap-override descriptors adjust the display of a font declared in an @font-face statement. This can help make fallback fonts look the same size.
Forced colors: The forced-colors CSS @media rule detects when a user has chosen to use a forced colors mode, also known as high-contrast mode, and the forced-color-adjust CSS property sets whether forced colors apply to an element.
image-set(): The image-set() CSS function provides a set of images at different resolutions or pixel densities, which the browser can pick from, depending on the device capabilities.
Top-level await: The await keyword, when used at the top level of a module (outside of an async function), delays parent module execution until after a promise fulfills.
Fixed-width SIMD (WebAssembly): 128-bit SIMD (Single Instruction Multiple Data) performs one instruction on multiple units of data, when running on hardware that supports such instructions. Also known as vector instructions.

New in Firefox for Android

The following features are now available in Firefox for Android:

aspect-ratio: The aspect-ratio CSS property controls the width-to-height ratio of elements. For <img> and <video> elements, the width and height attributes used together with height: auto control the aspect ratio while the image/video is loading.
Event timing: The event and first-input performance entries and the PerformanceEventTiming API measures the latency of user input events, such as mouse clicks or keypresses, and the latency of the first user input. First Input Delay (FID) is a common metric for perceived responsiveness.
Font metric overrides: The ascent-override, descent-override, and line-gap-override descriptors adjust the display of a font declared in an @font-face statement. This can help make fallback fonts look the same size.
Forced colors: The forced-colors CSS @media rule detects when a user has chosen to use a forced colors mode, also known as high-contrast mode, and the forced-color-adjust CSS property sets whether forced colors apply to an element.
image-set(): The image-set() CSS function provides a set of images at different resolutions or pixel densities, which the browser can pick from, depending on the device capabilities.
Top-level await: The await keyword, when used at the top level of a module (outside of an async function), delays parent module execution until after a promise fulfills.
Fixed-width SIMD (WebAssembly): 128-bit SIMD (Single Instruction Multiple Data) performs one instruction on multiple units of data, when running on hardware that supports such instructions. Also known as vector instructions.