Firefox 73 is upon us

Another month, another new browser release! Today we’ve released Firefox 73, with useful additions that include CSS and JavaScript updates, and numerous DevTools improvements.

Read on for the highlights. To find the full list of additions, check out the following links:

Note: Until recently, this post mentioned the new form method requestSubmit() being enabled in Firefox 73. It has come to light that requestSubmit() is in fact currently behind a flag, and targetted for a release in Firefox 75. Apologies for the error. (Updated Friday, 14 February.)

Web platform language features

Our latest Firefox offers a fair share of new web platform additions; let’s review the highlights now.

We’ve added to CSS logical properties, with overscroll-behavior-block and overscroll-behavior-inline.

These new properties provide a logical alternative to overscroll-behavior-x and overscroll-behavior-y, which allow you to control the browser’s behavior when the boundary of a scrolling area is reached.

The yearName and relatedYear fields are now available in the DateTimeFormat.prototype.formatToParts() method. This enables useful formatting options for CJK (Chinese, Japanese, Korean) calendars.

DevTools updates

There are several interesting DevTools updates in this release. Upcoming features can be previewed now in Firefox DevEdition.

We continually survey DevTools users for input, often from our @FirefoxDevTools Twitter account. Many useful updates come about as a result. For example, thanks to your feedback on one of those surveys, it is now possible to copy cleaner CSS snippets out of the Inspector’s Changes panel. The + and - signs in the output are no longer part of the copied text.

Solid & Fast

The DevTools engineering work for this release focused on pushing performace forward. We made the process of collecting fast-firing requests in the Network panel a lot more lightweight, which made the UI snappier. In the same vein, large source-mapped scripts now load much, much faster in the Debugger and cause less strain on the Console as well.

Loading the right sources in the Debugger is not straightforward when the DevTools are opened on a loaded page. In fact, modern browsers are too good at purging original files when they are parsed, rendered, or executed, and no longer needed. Firefox 73 makes script loading a lot more reliable and ensures you get the right file to debug.

Smarter Console

Console script authoring and logging gained some quality of life improvements. To date, CORS network errors have been shown as warnings, making them too easy to overlook when resources could not load. Now they are correctly reported as errors, not warnings, to give them the visibility they deserve.

Variables declared in the expression will now be included in the autocomplete. This change makes it easier to author longer snippets in the multi-line editor. Furthermore, the DevTools setting for auto-closing brackets is now working in the Console as well, bringing you closer to the experience of authoring in an IDE.

Did you know that console logs can be styled using backgrounds? For even more variety, you can add images, using data-uris. This feature is now working in Firefox, so don’t hesitate to get creative. For example, we tried this in one of our Fetch examples:

console.log('There has been a problem with your fetch operation: %c' +
e.message, 'color: red; padding: 2px 2px 2px 20px; background: yellow 3px no-repeat

And got the following result:

styled console message with yellow highlighter effect

We’d like to thank Firefox DevTools contributor Edward Billington for the data-uri support!

We now show arguments by default. We believe this makes logging JavaScript functions a bit more intuitive.

And finally for this section, when you perform a text or regex search in the Console, you can negate a search item by prefixing it with ‘-’ (i.e. return results not including this term).

WebSocket Inspector improvements

The WebSocket inspector that shipped in Firefox 71 now nicely prints WAMP-formatted messages (in JSON, MsgPack, and CBOR flavors).

a screencapture showing WAMP MessagPack in the WebSocket Inspector

You won’t needlessly wait for updates, as the Inspector now also indicates when a WebSocket connection is closed.

A big thanks to contributor Elad Zelingher for implementing the WAMP support, and to saihemanth9019 for the WebSocket closed indicator!

New (power-)user features

We wanted to mention a couple of nice power user Preferences features dropping in Firefox 73.

First of all, the General tab in Preferences now has a Zoom tool. You can use this feature to set the magnification level applied to all pages you load. You can also specify whether all page contents should be enlarged, or only text. We know this is a hugely popular feature because of the number of extensions that offer this functionality. Selective zoom as a native feature is a huge boon to users.

The DNS over HTTPS control in the Network Settings tab includes a new provider option, NextDNS. Previously, Cloudflare was the only available option.

About Chris Mills

Chris Mills is a senior tech writer at Mozilla, where he writes docs and demos about open web apps, HTML/CSS/JavaScript, A11y, WebAssembly, and more. He loves tinkering around with web technologies, and gives occasional tech talks at conferences and universities. He used to work for Opera and W3C, and enjoys playing heavy metal drums and drinking good beer. He lives near Manchester, UK, with his good lady and three beautiful children.

More articles by Chris Mills…


  1. Virendra kumar

    How do we know when to use the new Firefox ?

    February 11th, 2020 at 09:10

  2. Ceremy Jorbyn

    No doubt I’ll have to fiddle around with the userstyle CSS just to get the bloody tabs on the bottom again. Annoying. Just make it a toggle ffs.

    February 11th, 2020 at 18:14

  3. Michael M.

    I see in the release notes: “Improved auto-detection of legacy text encodings on old web pages which don’t explicitly declare the text encoding.” I can’t find the Bugzilla entry for this, so I’m not sure what has been done and what should change, but I note that at least for xkcd it’s not an improvement, e.g. see the title text in (at least I assume that before Firefox detected UTF-8 correctly for that page and only now switched to ISO-whatever).

    February 12th, 2020 at 01:49

  4. Michael Jones

    Firefox 73.0 does not work, all I can do is open tabs, customise header and that is it. I have tried refreshing, downloading, uninstalling and downloading nothing works.

    February 12th, 2020 at 05:06

    1. Jon Paddock

      Michael I feel your pain…I’m having the exact same problems. Only the headers are showing but nothing but a dark blank area below where the web pages should show up. After the 73.0 update Firefox isn’t working for me. I’ve switched back to Chrome for the time being.

      February 17th, 2020 at 22:41

  5. Michael Jones

    I did forget to mention in my first post that firefox does not even connect to the internet.

    February 12th, 2020 at 05:15

  6. Trevor Baaird

    Yep Firefox update does not work – same as Michael…………….

    February 12th, 2020 at 07:49

    1. Chris Mills

      Hrm, I wonder if you and Michael have a particular OS/browser combination that is having a problem? If there is a problem, it has probably already been reported by now. Maybe worth checking to see if others have reported the problem?

      February 12th, 2020 at 08:04

      1. Trevor Baird

        Checked over there and the very “clever” people say that there is a problem.

        February 13th, 2020 at 01:01

        1. Annika S

          HI trevor,
          you have a incident number? i cant find anything on bugzilla.. or i am not looking right. But I have the same issue, basically white blank pages and no network connection.


          February 14th, 2020 at 10:43


    Following update to 73 there is no connection to any selected web site including Mozilla. I’m sending this via Chrome from the same laptop.

    February 12th, 2020 at 13:57

  8. Eddy

    Firefox does not work for me. Same problem as Michael Jones: “Firefox 73.0 does not work, all I can do is open tabs, customise header and that is it”

    Hope it gets fixed SOON.

    February 12th, 2020 at 18:47

  9. Tim Rowe

    Whenever I tried to open this website through firefox –
    firefox got crashed and I already report this bug so many times and I didn’t get any notifications.
    Kindly have a quick review.
    Lots of Regards,

    February 13th, 2020 at 04:01

  10. Yan


    I reported my update was working well.
    My OS is windows 10.

    February 13th, 2020 at 08:14

  11. Greg

    In earlier versions of FF I used the file “chrome://browser/content/places/bookmarksPanel.xul” as my home page, which displayed all my bookmarks grouped in various folders. In FF 73.0 this appears to be broken, giving a “File not found” error with the text “Firefox can’t find the file at jar:file:///C:/Program Files/Mozilla Firefox/browser/omni.ja!/chrome/browser/content/browser/places/bookmarksPanel.xul”. I have tried a clean install without any effect. Otherwise FF works as expected.

    Windows 10
    Firefox 73.0 (64-bit)

    February 13th, 2020 at 13:57

  12. Greg

    Addendum to previous comment: FF 73.0 can’t open any chrome: URLs.

    February 13th, 2020 at 14:13

  13. B

    Hi Chris, thanks for the update.
    Could you possibly whisper into a product manager’s ear that many users want their tabs to display below the address bar? Every new version means having to figure out how to update the css file.

    It’s baffling why your designers insist on this unwanted UX.


    February 15th, 2020 at 03:44

  14. Greg

    To answer my own question of Feb 13, in FF 73.0 formerly .xul files have been renamed .xhtml and relocated inside the omni.ja archive in the program folder. The proper way to display all bookmarks on one page or tab should be to point the browser to “chrome://browser/content/places/bookmarksSidebar.xhtml” instead of what I had been trying.


    February 16th, 2020 at 17:17

  15. User # 1,484,654,981

    “about:config?filter=permissions.default.image” set to 2 no longer works since the update. Images still load. Now what?

    March 4th, 2020 at 12:26

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