Firefox 90 release notes for developers

This article provides information about the changes in Firefox 90 that will affect developers. Firefox 90 was released on July 13th, 2021.

[!NOTE] See also Getting lively with Firefox 90 on Mozilla Hacks.

Changes for web developers

Developer Tools

• The response view now shows a preview for web fonts (Firefox bug 872078).

HTML

• A fix to the way that form payloads are handled around newline normalization and escaping in multipart/formdata. This meets the updated specification, and matches other browser implementations. (Firefox bug 1686765).
• Firefox now sets an image's {{Glossary("intrinsic size")}} and resolution based on {{Glossary("EXIF")}} information (if present and self-consistent). This allows a server to, for example, send a low-quality placeholder image to speed up loading. It also enables a number of other use cases (Firefox bug 1680387).

CSS

• -webkit-image-set() has been implemented as an alias of the standard {{cssxref("image/image-set", "image/image-set()")}} function (Firefox bug 1709415).

JavaScript

• Private class static and instance fields and methods are now supported by default (Firefox bug 1708235 and Firefox bug 1708236).
• The in operator can now be used to check if a class private method or field has been defined. This offers a more compact approach for handling potentially undefined features, as oppose to wrapping code in try/catch blocks (Firefox bug 1648090).
• Custom date/time formats specified as options to the Intl.DateTimeFormat() constructor can now include dayPeriod — a value indicating that the approximate time of day (e.g., "in the morning", "at night", etc.) should be included as a narrow, short, or long string (Firefox bug 1645115).
• The relative indexing method at() has been added to the Array, String and TypedArray global objects. (Firefox bug 1681371)

HTTP

• The HTTP {{Glossary("Fetch metadata request header", "fetch metadata request headers")}} (Sec-Fetch-*) are now supported. These headers provide servers with additional context about requests, including whether they are same-origin, cross-origin, same-site, or user-initiated, and where/how the requested data is to be used. This allows servers to mitigate against several types of cross-origin attacks (Firefox bug 1695911).

Removals

• FTP has now been removed from Firefox (Firefox bug 1574475). This follows deprecation in Firefox 88. Note that web extensions can still register themselves as FTP protocol handlers.

APIs

DOM

• Support was added for the deprecated {{DOMxref("WheelEvent")}} properties: WheelEvent.wheelDelta, WheelEvent.wheelDeltaX, and WheelEvent.wheelDeltaY. This allows Firefox to work with a small subset of pages that were broken by recent compatibility improvements to WheelEvent (Firefox bug 1708829).
• The {{domxref("CanvasRenderingContext2D")}} interface of the Canvas API now provides a {{domxref('CanvasRenderingContext2D.createConicGradient()','createConicGradient()')}} method. This returns a {{domxref('CanvasGradient')}} much like the existing {{domxref('CanvasRenderingContext2D.createLinearGradient()','linear')}} and {{domxref('CanvasRenderingContext2D.createRadialGradient()','radial')}} gradients, but allows a gradient to move around a point defined by coordinates. See Firefox bug 1627014 for more details.
• Support for the matrix protocol has been added and can now be passed into the {{domxref('Navigator.registerProtocolHandler()')}} method as a valid scheme.

WebDriver conformance (Marionette)

• Marionette now restricts to a single active WebDriver session (Firefox bug 1691047).
• Added support for the new type of user prompts in Firefox (Firefox bug 1686741)
• Window handles make use of a unique id now, and don't change for process swaps as caused by cross-group navigations (Firefox bug 1680479).
• Fixed an inappropriate abortion of the current WebDriver command when a new user prompt was opened in a background tab (Firefox bug 1701686).
• Fixed the WebDriver:GetWindowHandles command to now correctly handle unloaded tabs (Firefox bug 1682062).
• Fixed the WebDriver:NewSession command to always return the proxy capability even if empty (Firefox bug 1710935).

Removals

• With the removal of the FTP support in Firefox 90 the ftpProxy capability is no longer evaluated, and when used will throw an invalid argument error (Firefox bug 1703805).

Changes for add-on developers

• The matrix URI scheme is now supported and can be defined as a protocol within the protocol_handlers key in an extensions manifest.json
• Starting with this version, the Cache API can be used in the extension pages and worker globals. For more details, see (Firefox bug 1575625).