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Firefox Release Notes

Release Notes tell you what’s new in Firefox. As always, we welcome your feedback. You can also file a bug in Bugzilla or see the system requirements of this release.

101.0 Firefox Release

May 31, 2022

Version 101.0, first offered to Release channel users on May 31, 2022

We’d like to extend a special thank you to all of the new Mozillians who contributed to this release of Firefox!


  • Reading is now easier with the prefers-contrast media query, which allows sites to detect if the user has requested that web content is presented with a higher (or lower) contrast.

  • It’s your choice! All non-configured MIME types can now be assigned a custom action upon download completion.

  • Firefox now allows users to use as many microphones as you want, at the same time, during video conferencing. The most exciting benefit is that you can easily switch your microphones at any time (if your conferencing service provider enables this flexibility).



  • Removed "subject common name" fallback support from certificate validation. This fallback mode was previously enabled only for manually installed certificates. The CA Browser Forum Baseline Requirements have required the presence of the "subjectAltName" extension since 2012, and use of the subject common name was deprecated in RFC 2818.



  • Inspector panel: When adding/removing a class name to/from an existing HTML element (using .cls button in Rules View), an autocomplete drop down automatically offers all existing class names on the page. In Firefox 101 the selected class name in the autocomplete drop-down list is auto-applied immediately as the user changes the selection of the autocomplete list (using up/down arrow keys). This is especially useful for quick testing of various styles.

  • Inspector panel: This new option can be used to disable “drag to update” features in the Rule View (values of some CSS properties e.g., sizes can be modified by dragging the mouse horizontally).

    Screenshot showing Inspector Panel drag to update option checkbox

  • WebDriver BiDi: This protocol is enabled on the release channel to support external tools such as Selenium, which plan to start using WebDriver BiDi for Firefox. WebDriver-BiDi aims to provide a cross-browser protocol for browser automation that meets the requirements of modern web application testing tools. This allows both the client and the server to send & receive requests and responses.

Web Platform

  • Firefox new has added support for large, small, dynamic viewport units and logical ones (*vi and *vb). This gives users the flexibility to choose whether page elements are sized to the “smallest” viewport size (dynamic toolbar visible), “largest” viewport size (dynamic toolbar hidden), or “dynamic” viewport size (based on current status of dynamic toolbar).

  • Firefox 101 features added web conferencing support for enumerating (reducing errors caused by transposing or mistyping numbers) and selecting multiple audio input devices (giving you the ability to record or process multiple separate audio sources together, synchronously, at once) through navigator.mediaDevices.enumerateDevices().

Community Contributions

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