Firefox 91 release overview: new ESR base, Simplified Printing, new HTTPS-First Policy

Firefox 91 is the latest stable version of the web browser. Released on August 10, 2021, it is replacing Firefox 90 and previous versions of the stable branch of the browser.

All other Firefox release channels have been updated as well. Firefox Beta and Developer are moved to version 92, Firefox Nightly to version 93, and Firefox for Android will be moved to version 91 as well (a bit later, usually.

Firefox ESR is moving to a new base. Firefox 91 ESR is the new base which will replace Firefox 78 ESR in October (both run parallel for two releases).

Check out the Firefox 90 release overview to read up on the changes in Firefox 90.

Executive Summary

  • Firefox 91 is the new base for Extended Support Releases. It is supported for about a year with the released feature set.
  • Support for Windows single sign-on added.
  • HTTPS-First Policy in Private Browsing mode.
  • Firefox ESR 78.x is the last Firefox version that supports Flash officially. Support for it ends on October 10, 2021.
  • Firefox ESR 78.x is the last that supports Mac OS 10.12 or older.

Firefox 91.0 download and update

firefox 91.0 release

Firefox 91.0 is rolled out to all desktop systems starting August 10, 2021. Most Firefox installations are configured to download and install browser updates automatically.

You may select Menu > Help About Firefox to run a manual check.

Manual downloads are also available. The following pages list direct downloads for supported Firefox channels.

New features and improvements

HTTPS-First Policy

Firefox will try to connect using HTTPS first when in private browsing mode. The browser falls back to HTTP only if a HTTPS connection is not available.

Firefox supports a HTTPS-Only Mode which users may configure to prioritize HTTPS always. The browser displays a warning page if HTTPS is not supported by a server. Options to use HTTP are then provided.

Firefox users who enable HTTPS-Only Mode in private browsing mode, or in all modes, get the same functionality.

Simplify Printing restored

firefox simplified printing

Mozilla introduced a new printing interface in Firefox 81. Simplified Printing, an option to turn the content into a bare-bones version optimized for printing, was removed in that update.

Simplified printing displays a version of the page based on the browser's Reader View feature. The focus is on the article and related content such as images; menus, advertisement, other blocks on the site are not displayed in the mode.

Firefox 91 restores the option, and you may once again select it in the print dialog.

You can check out our full overview of simplified printing in Firefox 91 here.

Other changes

  • Firefox supports signing-in to Microsoft work and school accounts using Windows single sign-on (on Windows, obviously).
  • Total Cookie Protection improvements that update the cookie clearing logic and reveal to users which websites are storing information locally.
  • New locale Scots (sco) added.
  • Firefox enables High Contrast Mode on Mac OS automatically if "Increase Contrast" is checked.
  • 10%-20% increase in most user interactions thanks to "catch-up paints".
  • New file downloading behavior. All downloads are saved to the default directory or selected directory, even if "open" is selected.
  • Switch to Tab results in Firefox's address bar in Private Browsing windows (previously only in regular browsing windows).

Developer Changes

  • The Gamepad API requires a secure context starting in Firefox 91.
  • Visual Viewport API is supported by desktop versions of Firefox.
  • Intl.DateTimeFormat.prototype.formatRange() and Intl.DateTimeFormat.prototype.formatRangeToParts() are now supported in release builds
  • The Error() constructor can now take the error cause as value in the option parameter.
  • Window.clientInformation has been added as an alias for Window.navigator.

Enterprise changes

  • Support for Enterprise policies for Linux Snap users.
  • WindowsSSO policy added to enable or disable the Single Sign-On feature on Windows.
  • SearchEngines policy update supports setting the query charset. It defaults to UTF-8 instead of windows-1252 now.

Known Issues

None listed.

Security updates / fixes

Security updates are revealed after the official release of the web browser. You find the information published here after release.

Outlook

Firefox 92 will be released on September 7, 2021. Two Firefox 78.x ESR versions will be released in the coming months: Firefox 78.14 ESR in September, and the last 78.x release, Firefox 78.15 ESR in October.

Recently Reviewed Firefox extensions

Recent Firefox news and tips

Additional information / sources

Summary
Firefox 91 release overview: new ESR base, Simplified Printing, new HTTPS-First Policy
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Firefox 91 release overview: new ESR base, Simplified Printing, new HTTPS-First Policy
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Firefox 91 is the latest stable version of the web browser. Released on August 10, 2021, it is replacing Firefox 90 and previous versions of the stable branch of the browser.
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Comments

  1. Emmet_Brickowski said on August 10, 2021 at 8:23 am
    Reply

    SO AWESOME

    Back to only four weeks between awesomeness updates

    ETP dynamic First Party Isolation improvements, lots of new Smart Blocking shims (none of those limited global switches like Brave), and now ESR users can get in on the act – full on site data and networking isolation really is a game changer. Lucy says these are “real solutions” and she should know. Even Brave said they’re awesome.

    Add in uBlock Origin, which works best in Firefox with cname cloaking, and Firefox is absolutely the most private, configurable and totally AWESOME browser ever

    Lots of love, Emmet & Lucy xxx

  2. ilev said on August 10, 2021 at 11:00 am
    Reply
  3. Alex said on August 10, 2021 at 11:05 am
    Reply

    > New file downloading behavior. All downloads are saved to the default directory or selected directory, even if “open” is selected.

    This works only if “browser.download.improvements_to_download_panel” pref is turned on. This pref was added in Firefox 90 and turned off by default.

    Thus, this behavior will only work when the new download panel is enabled by default in a some future release. Therefore, I advise you to remove this from the changelog and correct the https://staging-ghacksnet.kinsta.cloud/2021/08/04/a-close-look-at-firefox-91s-new-file-download-opening-behavior/ post as it misleads readers

  4. Heydrich said on August 10, 2021 at 11:42 am
    Reply

    @Emmet_Brickowski:

    How true!

  5. meh said on August 10, 2021 at 12:14 pm
    Reply

    Does 91 esr retain proton.ednable in about:config or has this been removed?

    1. Yuliya said on August 10, 2021 at 1:59 pm
      Reply

      browser.aboutwelcome.protonDesign false
      browser.proton.enabled false
      browser.proton.places-tooltip.enabled false
      browser.proton.toolbar.version 3

      But they do nothing, still uglyness.

    2. ULBoom said on August 10, 2021 at 8:18 pm
      Reply

      It worked on v 90 when I tried it a few months ago in beta. Made the interface smaller, back to the compact version. Still had the skinny graphics that may not even display on poor displays with some themes.

      Some themes fatten graphics, kind of a treasure hunt finding a good one.

  6. computer said no said on August 10, 2021 at 1:58 pm
    Reply

    I am having performance issues with firefox and the CPU usage is unacceptable on my oldish laptop.
    Using chromium for now which runs better until i upgrade my computer.
    I am a puppy linux user.

    1. Anonymous said on August 11, 2021 at 7:24 pm
      Reply

      YES! Performance is so much worse with the later versions now. I can’t remember when it happened, maybe after 88 or something…

  7. StuckInside said on August 10, 2021 at 5:49 pm
    Reply

    After FF 89, someone posted that you could go to about:config and change browser.proton.contextmenus.enabled to “false” and get more compact context menus. That is now gone. I don’t mess around with .css files but someone on Reddit posted that those were a solution to get compact context menus as well, and that also no longer works.

    Any other ideas?

    1. ULBoom said on August 10, 2021 at 8:29 pm
      Reply

      Add it. And whatever others you want. Let us know the results.

      Copy/paste that preference into the about:config Search preference name box, pick boolean false then hit the + on the far right.

      May want to make

      browser.preferences.instantApply true

      to see results instantly. Works for almost all preferences, some need restarts.

  8. Anonymous said on August 10, 2021 at 6:10 pm
    Reply

    Anyone knows how to get rid of Firefox ugly new design?

    1. @Anonymous said on August 11, 2021 at 12:40 pm
      Reply
  9. Anonymous said on August 10, 2021 at 6:12 pm
    Reply

    Looks like rip off Chrome print dialog. Does Mozilla have anything original anymore?

  10. owl said on August 10, 2021 at 7:29 pm
    Reply

    And finally, in an ESR, here comes the forced proton interface. Fuck you, mozilla.

    1. rrady said on August 10, 2021 at 8:24 pm
      Reply

      Agree, fuck you, mozilla!!!

  11. Tony said on August 10, 2021 at 7:49 pm
    Reply

    Tried out 89.0 and hate the new look and removal of icons among many other things.And on top of that i experienced more crashes on 89.0 than i did the previous 3-4 years with any other FF versions.I’m staying on 88.0.1 and probably will be for a very long time.I just can’t be bothered to add back features nearly every update(downgrade) and revert their crap decisions.If all else fails i go to my backup browser of choice and probably won’t look back.

    1. ULBoom said on August 10, 2021 at 8:43 pm
      Reply

      Try uninstalling the old then installing the new version. After running the uninstaller, search for anything Mozilla and Firefox and delete it before the install. All folders, files, everything.

      I had exactly that issue a few months ago, constant weird certificate errors that refresh and normal reinstalls didn’t fix leading to freezes. Even saved profiles didn’t work. Still don’t know what caused it but a scorched earth uninstall fixed it. Pulled my saved prefs.js file over into the new profile to avoid hours in about:config. All else was obliterated.

      I had been doing a lot of experimenting with encrypted DNS in our router and the browser along with playing with a number of extensions and certs for our Linux LAN devices, went to 21H1 Win, so I probably hosed FF unknowingly.

  12. BeenNizeSYL said on August 10, 2021 at 9:14 pm
    Reply

    So after Oct 2021 even ESR editions will have the madness as well so time to look for an alternative web browser!

  13. Peter said on August 10, 2021 at 9:32 pm
    Reply

    Why do you have to keep doing this? I don’t get what Mozilla gains by pissing everyone off with removing the ability to disable proton. I just don’t understand.

  14. jmro said on August 10, 2021 at 11:36 pm
    Reply

    Thank you black7375 for Lepton (old name: Proton Fix)
    https://github.com/black7375/Firefox-UI-Fix
    Disclaimer: It works on Firefox 89 and above! (yes works for me, 91.0).

  15. Anonymous said on August 11, 2021 at 1:55 am
    Reply

    rather nice!

  16. Fuck you, mozilla said on August 11, 2021 at 2:23 am
    Reply

    >And finally, in an ESR, here comes the forced proton interface. Fuck you, mozilla.

    ROFL!

  17. hugh said on August 11, 2021 at 4:05 am
    Reply

    I had to turn off hardware acceleration to view video content in streaming media – Netflix and Youtube as examples.

    I’ve never had to do that before, ever.

  18. yanta said on August 11, 2021 at 5:08 am
    Reply

    OMG! This browser is an unmitigated disaster. This is going to b fun (/sarc), trying to get this back to a workable browser. I wish dev of programs would stop chaning UIs every new release. Have they nothing better to do or are they just trying to justify their existence?

    Ok, a serious question – if there a new GPO for the new ESR release? Can’t seem to find it. Anyone have links?

  19. Doug D said on August 11, 2021 at 7:58 am
    Reply

    Works perfect for me. Not a single issue. A little faster than the last version. Love it. Thanks Mozilla!

  20. KA Lynch said on August 11, 2021 at 3:11 pm
    Reply

    **Compact Mode** in the menus now ***screwed up*** again. The previous settings used after the v89 catastrophe :
    browser.compact true
    browser.compactmode.show true

    no longer have an effect, nor does the previous selection “density compact not supported” under “more tools.” I had all these set in V89.

    The following settings suddenly appeared additionally on searching for compact on about.config, haven’t the least idea what they mean. But no effect on menu density

    javascript.options.compact_on_user_inactive true
    javascript.options.compact_on_user_inactive_delay 300000
    javascript.options.mem.gc_compacting true

    It’s so AWESOME having to scroll down 3 screens instead of none on a 69 cm monitor to find menu items, Right.? so COOL man.

    1. Loxia said on August 11, 2021 at 4:20 pm
      Reply

      This userChrome.css code get the menus compact:

      /*** REDUCING VERTICAL SPACING IN MENUS ***/

      menupopup > menuitem, menupopup > menu {
      padding-block: 3px !important;
      }
      :root {
      –arrowpanel-menuitem-padding: 3px 6px !important;
      }

      Other CSS code to revert Proton can be found here:

      https://www.userchrome.org/firefox-89-styling-proton-ui.html

      1. KA Lynch said on August 11, 2021 at 5:40 pm
        Reply

        @Loxia —Thank you very much for the reply and the link.
        I am computer literate enough to insert short pieces of code somewhere in principle, but unfortunately I have no idea how to implement “userChrome.css” in the Firefox v91 browser.

      2. Loxia said on August 11, 2021 at 6:05 pm
        Reply

        Here is a “how-to” for creating a userChrome.css file:

        https://www.userchrome.org/how-create-userchrome-css.html

      3. KA Lynch said on August 11, 2021 at 6:33 pm
        Reply

        @Loxia Great, thanks! That worked.
        I created a “chrome” subfolder in the FF profile folder as instructed in the link, and then added the “userchrome.css” file using notepad++.
        I inserted your text and reduced the padding block parameter to 1 px. That seems to have produced a much narrower menu item spacing more like pre-v89.
        I have left the “arrowpanel-menuitem-padding” item as it stands for now (3px 6px).
        Thanks again.

  21. Anonymous said on August 12, 2021 at 12:31 am
    Reply

    The 91st release was the last straw forcing me to ditch FireFox after it enforced that ugly proton. Pathetic development.

  22. ms600 said on August 12, 2021 at 4:50 am
    Reply

    I am now unable to apply the container color line on top or at the bottom of the tabs using the userChrome.css file. Any help?

    1. ms600 said on August 12, 2021 at 6:37 am
      Reply

      Only found a script for color line at icon’s bottom.

    2. ms600 said on August 12, 2021 at 8:26 am
      Reply

      Solved.

  23. max3 said on August 13, 2021 at 3:26 am
    Reply

    I am still running a locked down 68.12.0 ESR with a handful of extensions, SimpleMenuWizard plus a sweetly modified about:config and I have never been happier. I also keep an auto-updated profile (now 91) just to keep an eye on the current changes, but I always come back to 68.

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