Firefox 81 release notes for developers

Changes for web developers

Developer Tools

• The Debugger now uses the TypeScript icon for .ts and .tsx files (Firefox bug 1642769). Previously a generic file icon was used.
• We've added support for line wrapping in the Debugger source pane (Firefox bug 1590885).
• We've removed unnecessary color vision simulations (protanomaly, deuteranomaly, and tritanomaly) from the Accessibility Inspector, and added a simulation for achromatopsia (no color) (Firefox bug 1655053).
• Autocompletion is now supported when adding a class to an element. Offered classes are based on existing classes in the document (Firefox bug 1492797).

HTML

• Automatic downloads are now blocked in a sandboxed <iframe> element (Firefox bug 1558394).

Removals

• Support for the non-standard mozallowfullscreen attribute has been removed from <iframe>. Consider using allow="fullscreen" instead (Firefox bug 1657599).

CSS

• We now support the value of clip for the overflow property, via renaming overflow: -moz-hidden-unscrollable (Firefox bug 1531609).
• The text-combine-upright property has been made non-animatable to comply with the spec (Firefox bug 1654195).

Removals

• The non-standard ::-moz-focus-outer pseudo-element has been removed (Firefox bug 1655859).

JavaScript

No changes.

HTTP

• Firefox now accepts non-standard Content-Disposition headers with an unquoted filename containing spaces (Firefox bug 1440677).
• Firefox now supports the HTTP Feature-Policy header's web-share directive, which can be used to restrict access to the Web Share API to trusted origins. Note that Firefox does not support the Web Share API itself, at time of writing (Firefox bug 1653199).

APIs

Gamepad

• The threshold for gamepad joystick activation has been increased. This reduces the chance of inadvertent gamepad activation, both from controllers that send small axis values when they are idle, and very small bumps. (Firefox bug 1539178)

Workers/Service workers

• Strict MIME type checks are now enforced on worker and shared worker scripts, i.e., scripts targeted by the Worker() and SharedWorker() constructors must now be served with text/javascript (Firefox bug 1569123).

WebDriver conformance (Marionette)

• The setWindowRect capability is now true by default for all desktop applications (including Thunderbird), and false on Android for GeckoView (Firefox bug 1650872).
• We've added Fission support for the following commands: WebDriver:SwitchToFrame, WebDriver:SwitchToParentFrame, WebDriver:GetCurrentURL. All Fission-compatible commands are only available when marionette.actors.enabled is set to true.
• Fixed the broken tracking of browsing contexts after opening a new window (Firefox bug 1661495).
• In case of failures WebDriver:SwitchToWindow now always returns a unified NoSuchWindowError (Firefox bug 1663429).

Removals

• WebDriver:GetActiveFrame has been removed, because it's not part of the WebDriver specification and is no longer used (Firefox bug 1659502).

Changes for add-on developers

• tabs.saveAsPDF() is now supported on macOS (Firefox bug 1653354).
• The behavior of webNavigation.getFrame() and webNavigation.getAllFrames() has changed. Moving forward, when a tab is discarded the promise will fulfill with a null value (Firefox bug 1654842).