Firefox 108 out with security fixes and Windows 11 efficiency mode support

Martin Brinkmann
Dec 13, 2022
Updated • Dec 13, 2022
Added information about the security updates.

Mozilla Firefox 108.0 Stable is the latest version of the Firefox web browser. The browser will be released today, alongside Firefox 102.6 ESR, the Extended Support Release.

Firefox 108 is a security update, but it makes a few changes and improvements to the browser that are not security related. Windows 11 users get support for efficiency mode, which is designed to reduce the resource usage of background tabs, and all users may use Shift-Esc to open the Process Manager of the browser.

All Firefox development channels, Firefox Beta, Dev and Nightly, do get a version bump at around the same time. Firefox Beta and Dev move to version 109 and Firefox Nightly to version 110. Firefox for Android follows the stable channel's version, which means that it is also updated to version 108.

Executive Summary

  • Firefox 108 is a security update. It addresses 8 unique security issues in the browser. The aggregate severity rating is high.
  • This version of Firefox is the last major release of 2022. The next release, Firefox 109, will be released in January 2022.

Firefox 108 download and update

Firefox 108's release date is December 13, 2022. Mozilla releases the browser on the day and the built-in updating system should pick up the update soon thereafter. Firefox users may speed up the installation of the update once the browser is released. This is done by select Menu > Help > About Firefox.

The installed version is displayed at this point and an update check is performed. The new version is then downloaded and installed immediately.

Here are the official download locations:

Firefox 108.0 new features and improvements

Firefox 108 is a small release. It is a security update first and foremost, but it includes some improvements that are not related to the browser's security.

You may remember that Mozilla introduced performance improvements for Windows 11 devices in Firefox 107. Firefox 108 continues the improvements, although unrelated to the changes in Firefox 107. The new version adds support for Windows 11's efficiency mode, which Microsoft introduced in the Windows 11 2022 Update.

The mode should not be confused with Microsoft Edge's Efficiency Mode feature. Both are designed to improve performance, but Windows 11's Efficiency Mode feature is available to all apps, regardless of whether they are browsers or not.

The mode is enabled automatically by Firefox. A quick check of the Windows Task Manager, using Ctrl-Shift-Esc, shows the Efficiency icon for some of Firefox's processes. This limits the resource use of these Firefox processes.

Other changes and fixes

process manager firefox

Firefox users may use the keyboard shortcut Shift-Esc to display the process manager of the browser. It lists all open processes and helps users find processes that use too many resources.

Mozilla notes in the release notes that frame scheduling under load has been improved. The change improves "Firefox's MotionMark scores" according to the organization.

Other changes listed in the release notes:

  • Support for ICCv4 profiles added to the firefox web browser.
  • Support for non-English characters when saving and printing PDF documents added.
  • Fixed an issue with Firefox's "Only show on new tab" default bookmark toolbar behavior.


  • Trigonometric functions are now enabled with the layout.css.trig.enabled preference set to true by default.
  • The <source> element supports height & width attributes when it is a child of a <picture> element.
  • CSS <calc-constant> type is implemented to allow for well-known constants such as pi and e within math functions
  • Container query length units are now supported via the the layout.css.container-queries.enabled preference, which is set to false by default.
  • Content-Security-Policy HTTP header directives style-src-elem and style-src-attr are now supported.
  • Content-Security-Policy HTTP header directives script-src-elem and script-src-attr are now supported.
  • The Web MIDI API is now available in secure contexts.
  • Added support for the browsingContext.domContentLoaded event
  • Firefox now issues a warning when an extension is installed if its version number doesn't follow the recommended format.
  • Import maps, which allow web pages to control the behavior of JavaScript imports, are now enabled by default.

Enterprise changes

None published.

Known Issues

None listed.

Security updates / fixes

The following security issues are fixed in the release:

  1. CVE-2022-46879: Memory safety bugs fixed in Firefox 108
  2. CVE-2022-46878: Memory safety bugs fixed in Firefox 108 and Firefox ESR 102.6
  3. CVE-2022-46877: Fullscreen notification bypass
  4. CVE-2022-46875: Download Protections were bypassed by .atloc and .ftploc files on Mac OS
  5. CVE-2022-46874: Drag and Dropped Filenames could have been truncated to malicious extensions
  6. CVE-2022-46873: Firefox did not implement the CSP directive unsafe-hashes
  7. CVE-2022-46872: Arbitrary file read from a compromised content process
  8. CVE-2022-46871: libusrsctp library out of date


Firefox 109 Stable and Firefox 102.7 ESR will be released on January 17, 2023.

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Firefox 108 out with security fixes and Windows 11 efficiency mode support
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Firefox 108 out with security fixes and Windows 11 efficiency mode support
An overview of the Firefox 108 Stable release for all support operating systems, including information about its security updates.
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  1. tony said on December 14, 2022 at 7:16 pm

    I see they still have those buttons on top.No thanks.

  2. Fuffle said on December 14, 2022 at 5:05 pm

    Shame the update forced my default search provider back to Google, 1 second to fix, but a lasting reminder not to trust any dev.

  3. Chris said on December 14, 2022 at 11:58 am

    So amazing that the windows efficiency mode is enabled automatically by Firefox… Love it !

  4. Iron Heart said on December 14, 2022 at 8:27 am

    > Firefox 108 out with security fixes

    Impossible. I was told otherwise. I was told that Firefox is that hyper-secure browser that everyone should be using over Chromium, how can it have security issues? Shame on you, Mozilla!

    1. Mothy said on December 14, 2022 at 3:32 pm

      If you actually read the security advisory information they are rated “High” not “Critical”. Whereas Chrome often has numerous critical vulnerabilities many of which are known to be exploited in the wild.

    2. Yash said on December 14, 2022 at 9:42 am

      And I thought it was Chromium fanboys that fuelled this myth!

  5. Shiva said on December 13, 2022 at 4:04 pm


    I had to change the values of:

    #PersonalToolbar .toolbarbutton-1, toolbarbutton.bookmark-item:not(.subviewbutton){
    padding-left: …px !important;
    padding-right: …px !important;

    And the icon replacement no longer works for me:

    #……. {list-style-image: url(“data:image/svg+xml;base64,…”) !important;}

    1. Tom Hawack said on December 13, 2022 at 10:45 pm


      I’m facing CSS issues as well with latest Firefox 108.0.
      Others as well : “Having issues with custom CSS in 108.0 ? I do” at

      – Icons’ margin and perhaps padding have changed;
      – The icon replacement works here but I don’t set them with base64 but with a local url , i.e. :

      /* uBlock Origin */
      #ublock0_raymondhill_net-browser-action .toolbarbutton-icon {list-style-image: url(images/uBlock.png) !important;}

      Yet I’m facing issues when I set the icon replacement within a style condition :
      #ublock0_raymondhill_net-browser-action[style*=”icon_16-off”] .toolbarbutton-icon {list-style-image: url(images/uBlock-OFF.png) !important;}

      The latter no longer works. Bothering given this allows to change not only an extension’s default toolbar button but as well it’s specific icon with changing conditions.

      Reverted to FF107 until I find a solution because the icon issue is more than cosmetic : I need to have extensions’ buttons reflect their change … or leave default icons but 90% of them are graphically lousy, hard to find when you have over 40 of them on the toolbars …

      Good luck amigo :)

      1. Tom Hawack said on December 15, 2022 at 3:28 pm

        I finally found the explanation: “Firefox 108 broke all my toolbar and URL-bar icon tweaks : FirefoxCSS” AT

        “Extensions buttons in the toolbar are now wrapped into a element – the selectors you are using match that toolbaritem, but if you want to change the icon used then you need to target the actual button within that wrapper.”

        My above example:

        #ublock0_raymondhill_net-browser-action .toolbarbutton-icon {list-style-image: url(images/uBlock.png) !important;}
        #ublock0_raymondhill_net-browser-action[style*=”icon_16-off”] .toolbarbutton-icon {list-style-image: url(images/uBlock-OFF.png) !important;}


        #ublock0_raymondhill_net-BAP {list-style-image: url(images/uBlock.png) !important;}
        #ublock0_raymondhill_net-BAP[style*=”icon_16-off”] {list-style-image: url(images/uBlock-OFF.png) !important;}

        It works!

      2. Shiva said on December 14, 2022 at 9:17 am

        Hi Tom,

        about the icons replacement, they are related to some extensions. I solved yesterday: there is to update the ID (I checked via browser Toolbox).
        Today I have to take a look at CustomCSSforFx compact mode. What a pain when they change these things.

    2. toja said on December 13, 2022 at 7:16 pm

      I use Firefox ESR so that I don’t play with updates so often.
      I’ve been on Firefox version 102 since 2022-06-28, and will switch to Firefox version 115.3 from 2023-09-26.

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