Firefox 99 for developers

This article provides information about the changes in Firefox 99 that will affect developers. Firefox 99 was released on April 5, 2022.

Changes for web developers


No notable changes.


No notable changes.


No notable changes.


  • navigator.pdfViewerEnabled is now enabled, and is the recommended way to determine whether a browser supports inline display of PDF files when navigating to them. Sites that use the deprecated properties navigator.plugins and navigator.mimeTypes to infer PDF viewer support should now use the new property, even though these now return hard-coded mock values that match the signal provided by pdfViewerEnabled (Firefox bug 1720353).

Media, WebRTC, and Web Audio


  • The Network Information API was previously enabled on Android (only), but is now disabled by default on all platforms. This API is on the path for removal because it exposes a significant amount of user information that might be used for fingerprinting. (Firefox bug 1637922).

WebDriver conformance (Marionette)

  • Fixed a bug where the Shift key was not handled properly when part of a key sequence of the WebDriver:ElementSendKeys command (Firefox bug 1757636).

Changes for add-on developers

Older versions