Firefox 149 release notes for developers (Beta)

Changes for web developers

HTML

• The popover global attribute now supports the hint value. Popovers with the hint value will not close auto popovers when they are displayed, but will close other hint popovers. (Firefox bug 1867743).

APIs

DOM

• The CloseWatcher interface is now supported. This allows developers to implement components that can be closed using device-native mechanisms, such as the Esc on Windows or the Back key on Android, in the same way as built-in components such as dialogs and popovers. (Firefox bug 1966073).

Media, WebRTC, and Web Audio

• The captureStream() method of the HTMLMediaElement interface is now supported. This returns an object that streams the real-time capture of the content in the element. The stream can be used, for example, as a source for a WebRTC RTCPeerConnection. Previously, captureStream() was available only as the non-standard mozCaptureStream() method. (Firefox bug 2017708).

Changes for add-on developers

The ability of extensions to dynamically execute code in their moz-extension: documents with tabs.executeScript, tabs.insertCSS, tabs.removeCSS, scripting.executeScript, scripting.insertCSS, and scripting.removeCSS is deprecated. The feature is no longer available in Firefox Nightly, and the beta and release versions of Firefox provide a warning in the tab's console. This restriction will apply to all versions of Firefox 152 and later. As an alternative, an extension can run code in its documents dynamically by registering a runtime.onMessage listener in the document's script, then sending a message to trigger execution of the required code.(unsupported templ: bug)

Experimental web features

These features are shipping in Firefox 149 but are disabled by default. To experiment with them, search for the appropriate preference on the about:config page and set it to true. You can find more such features on the Experimental features page.