About:config is blocked in Firefox Preview Stable and Beta

Martin Brinkmann
Jan 6, 2020
Updated • Jan 13, 2020

Mozilla is working on a new mobile browser for Google's Android operating system. Called Firefox Preview currently, it is available as a preview version right now. As is the case with desktop Firefox, Firefox Preview for Android is available in different editions that differ in terms of stability and development progress.

Firefox Preview Stable is the main version that is comparable to Firefox Stable for desktop operating systems. There is also Firefox Preview Beta and Firefox Preview Nightly for Developers.

While there are not many major differences in regards to core functionality between the different editions usually, it appears that Mozilla decided to implement one in Firefox Preview that might irritate some users of Stable or Beta versions of the browser.

Firefox supported the internal about:config page for a long time; it provides an interface to make advanced configuration changes directly in the web browser. Firefox for the desktop and mobile supported it until now.

When you try to load about:config in Firefox Preview Stable or Firefox Preview Beta, you are greeted with a "cannot complete request" message instead.

The page states that "additional information about this problem or error is currently unavailable", and there is a "try again" button to retry loading the page.

firefox about config cannot complete request

It is unclear at this point if the change is deliberate or if Mozilla plans to unblock the page before final release. As it stands, Firefox Preview Stable and Beta users cannot make use of about:config to make changes to Firefox's configuration.

If you compare that to the current Firefox mobile browser for Android, which supports about:config, you have to wonder whether that is an intentional change or something that just has not been implemented yet.

It seems expected behavior judging from the post of a contributor on the official GitHub project website:

This is expected behavior from GeckoView. Fenix does not control access to it. When Fenix nightly is released it will have access to about:config for users that have that requirement.

Closing Words

It is probably not a good idea to release Firefox Stable or Beta versions for Android without support for about:config as users who used it in the past will certainly be disappointed that the feature is not available. It is also difficult to justify considering that the previous Firefox for Android supported it and desktop Firefox Stable supports it as well.

Now you: what is your take on this?

About:config is blocked in Firefox Preview Stable and Beta
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About:config is blocked in Firefox Preview Stable and Beta
When you try to load about:config in Firefox Preview Stable or Firefox Preview Beta, you are greeted with a "cannot complete request" message instead.  
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  1. beachbubba said on April 10, 2021 at 6:16 pm

    Taking away the ability to customize my Firefox browsing experience via about:config is like taking away democracy from a culture that’s never known anything else. I am outraged beyond words at Mozillas audacity and disregard for people who like to customize their browser to their own specific likes.

  2. Firezen said on June 14, 2020 at 5:04 pm

    Why? Now it really doesn’t load for me anymore in the Firefox Preview, holy moly, how annoying.
    I don’t want DoH nor context menu events, damnit!

    This is madness

  3. me said on January 13, 2020 at 4:29 pm

    That is, all the usual problems of using a marginal browser like firefox without any of its advantages in control and privacy. Nice work, Mozilla.

  4. Peterc said on January 9, 2020 at 1:23 am

    @Iron Heart:

    Yup. Pale Moon is definitely a small operation without the wherewithal to do everything on its own. In that sense, they are a little like downstream Linux distros that hitch their wagon to a major upstream distro. The difference is that downstream distros have multiple major upstream distros to choose from (Red Hat, Ubuntu, SUSE, Debian, and Arch), whereas in the open-source, “user-centric” browser arena, there is only one adequately staffed option (Firefox).

    But for now, Pale Moon’s developers are doing their best to keep the spirit and practice of pre-Australis, pre-Quantum, pre-WebExtensions Firefox — I almost wrote “pre-Google-Chrome” Firefox — alive, and in my view, they’re largely succeeding. I wish more web designers would stop coding exclusively for the very latest standards and protocols supported only by the very latest versions of Google Chrome (and sometimes Firefox as well), but Pale Moon handles the majority of pages I run into just fine. I also wish more legacy extension developers had migrated to Pale Moon instead of simply throwing in the towel when Mozilla pulled the plug on them, but at least the most important ones still work or have been forked.

    Anyway, I know Pale Moon may well be living on borrowed time, but I’m enjoying it while it lasts. (I suppose I should give Waterfox Classic honorable mention here, as it’s in the same boat as Pale Moon, but Waterfox has always been glitchier and more problematic for me than Pale Moon, particularly in Linux. Pale Moon has a couple of officially endorsed PPAs for Ubuntu-family distros, and the one I use has been kept religiously up to date and worked perfectly every time. I can’t say the same for Waterfox’s unofficial PPA.)

    1. New Tobin Paradigm said on January 11, 2020 at 7:17 am

      We will never stop, no matter what happens to Mozilla. We can’t because there would be nothing left to fall back on. Except maybe gardening, that is.

      Garden grown tomatos are awesome kinda like garden grown we browsers. We didn’t magic up the original seeds but with come care and experence we can grow really awesome web tomatos!

      1. New Tobin Paradigm said on January 11, 2020 at 7:19 am


    2. birmingham said on January 9, 2020 at 5:28 pm

      I share this view to a good part, especially that about so-called “web compatibility”, which is in reality not keeping it on “standards” but on browser exclusive site compatibility with google, fb and other monopoly aimed sites. And like everyone should know in the meantime, these browsers are designed for ad-friendly marketing and data collection.
      Despite of all obvious nonsense, fake information and death wishes, spread here and elsewhere, Pale Moon is still my main browser of choice and even if Google would make their services Chrome-exclusive I could use some third choice Chrome-clone for just that or quit using their services.
      This is another article about more reduced Firefox configuration options. I don’t care much about Mozilla decisions anymore as I quit using Firefox, more or less, for ages. Nonetheless I wish Firefox users a good time and Mozilla good luck with future changes, but in the end bashing on good browser alternatives will not change anything to the good for Firefox.

  5. Peterc said on January 8, 2020 at 3:46 am

    As a Pale Moon user who regularly gets dumped on for defending an “obsolete” browser that leaves its users fully in charge, I *could* take advantage of this article to post something snarky like, “You don’t see *Pale Moon* trying to pull this kind of bullshit” … but I’m *much* too gracious to do that. ;-)

    1. Iron Heart said on January 8, 2020 at 10:57 am


      Pale Moon and Firefox will both die at the same time, precisely when Firefox either gets close to 1% total market share or when Mozilla dumps Gecko in favor of Blink. Pale Moon is kept alive by the continued existence of Firefox, the PM devs also pull most web compatibility improvements from the Firefox main tree. If Firefox dies, Pale Moon dies as well.

  6. Bye Bye said on January 7, 2020 at 11:19 pm

    Last passable version was 52.9.0
    Last good version was 3.6.12

    Now I have set up Windows XP with the following browsers:
    Mypal (Pale Moon)
    Centaury (Basilisk)

    OS runs in Virtualbox – if you have some spare RAM it’s easy.

  7. Cain said on January 7, 2020 at 5:04 am

    Time for a new browser, maybe Bromite?

    1. Anonymous said on February 20, 2020 at 11:42 pm

      What control it will have more than FF?

      It is ridiculous that when mozilla do stupid decisions people say time to move to chrome or…

      Even FF without about:config have all options of chrome and become same in performance.

      Although the absence of about:config is terrible.

  8. ULBoom said on January 7, 2020 at 3:37 am

    Seems like a gliche. If not it’s silly, there are third party apps that moat mobile browsers well.

    Maybe it’s not representative but I don’t know anyone who uses browsers on their phone very often. Too small, constant scrolling, search results buried in ads, etc., totally different than browsing on a laptop or desktop.

    Others who almost never make calls on their phone (huh?!) but don’t really grasp that phones, being telecommunication devices are regulated differently from computers. Use it as a phone or not, privacy isn’t too good.

  9. JohnIL said on January 6, 2020 at 11:01 pm

    Besides Chrome all the other browsers are racing to be part of the bottom feeders of the browser world. Has Mozilla done anything in the last few years to reverse that trend for Firefox? No.

  10. Richard Steven Hack said on January 6, 2020 at 10:57 pm

    Mozilla is known for stupid decisions. ‘Nuff said.

  11. grandis said on January 6, 2020 at 8:10 pm

    Destroy the last strands of trust. Push corrosion in Linux kernel (rust).


    1. Anonymous said on January 9, 2020 at 3:23 pm

      @grandis: Linux kernel is written in the C programming language and assembly. Mozilla Firefox is written in – – – and Rust.


  12. Anonymous said on January 6, 2020 at 7:33 pm

    alot of .. unlucky moves from mozilla lately. lets see if they see the hints from the communit in time.

  13. notanon said on January 6, 2020 at 6:20 pm

    I’m not surprised.

    Designing a new browser in the current government mandated censorship environment necessitates more a more restrictive approach to comply with government (such as the European Union) laws about the internet & privacy (or lack of).

    We saw this last year, when the United Kingdom’s ISP’s tried to pressure Mozilla to prevent DNS-Over-HTTPS (DoH). Mozilla caved to the pressure, & the United Kingdom is the only country in the world where DoH is not used by default (because the UK loves to spy on their citizens).

    Merkel has introduced a draconian law that requires people to give the government their passwords, so they can go through everything you have ever posted/sent looking for “hate speech”, so they can throw you in the gulag (fortunately, it may not pass, even the Germans have a backbone sometimes [not about immigrants destroying their nation, unfortunately]).

    Mozilla probably is designing Fenix to comply with all the censorship laws that are currently being implemented.

    Hopefully, this won’t migrate to Firefox Desktop (America still has a 1st amendment [Free Speech], despite Silicon Valley trying to censor everything that doesn’t conform to their far left bias, so there shouldn’t be restrictions on Americans using Firefox).

    1. Stv said on January 7, 2020 at 8:47 am

      And you are proud of your gram pa’s SS clothing in the closet right?

      You don’t have to give your password, you have mistaken Germany with an african country (they can get your DB from site operators as usually) and they just watch your metadata to recognize you in the future if you dare to talk like this about human beings again.

      1. Vst said on January 7, 2020 at 11:05 pm

        @stv How do you know about gram pa’s clothes?

      2. notanon said on January 7, 2020 at 7:24 pm


        Calling everyone a Nazi??? Typical leftist, NPC behavior.

        And you’re WRONG.

        Merkel has introduce legislation that would require people to give their passwords to the government.

        Google & Bing exists, use it moron.

    2. MikeO said on January 6, 2020 at 6:45 pm

      “…requires people to give the government their passwords”

      To even consider such an idea is beyond outrageous.

  14. Sappiq said on January 6, 2020 at 4:41 pm

    Another nail in the coffin for Firefox and another step closer to becoming a Chrome clone I see, good work Mozilla, you’ve outdone yourselves again.

    I hope next time they disable the ability to change download location and pick search engine, because Mozilla always knows what’s best for it’s sheeple.

    1. Cor said on January 6, 2020 at 7:37 pm

      If Firefox could move its “Other bookmarks” to the bookmarks bar like Chrome that would be great.

  15. Johan Gustavsson said on January 6, 2020 at 4:37 pm

    How to show the old about:config menu:
    To display the old about:config interface, in the address bar type: chrome://global/content/config.xul.
    The list of entries displays immediately, there’s no warning page. If you want to continue to use the old interface you can bookmark it (Ctrl + D) instead of typing in the address every time.

    1. Anon said on January 7, 2020 at 11:28 pm

      Why does Firefox use the ‘chrome://’ flag if it doesn’t use Chromium?

      1. New Tobin Paradigm said on January 11, 2020 at 7:12 am

        The chrome pseudo-protocol is a Netscape convention meant to represent the true meaning of the word “chrome” in this context which is application user interface. This predate’s Google Chrome’s existance by some 7-9 years.

        Google’s use of the name Chrome was directly inspired by this usage in Mozilla.

        Such a shame that history and context is not more important is our modern lives, eh?

    2. glitsj16 said on January 6, 2020 at 11:56 pm

      FF71+ @ chrome://global/content/config.xul
      FF73+ @ chrome://global/content/config.xhtml

    3. ShintoPlasm said on January 6, 2020 at 5:06 pm

      This doesn’t work in my Firefox Preview “Stable”. @Martin: what version/edition did you try this on?

      1. Martin Brinkmann said on January 6, 2020 at 5:32 pm

        I think this is only for desktop.

    4. Martin Brinkmann said on January 6, 2020 at 4:40 pm

      Great tip, thanks Johan!

      1. T said on January 6, 2020 at 6:37 pm


        Does not seem to work either at lease in the 3.0.1 build 13502256

        Both lead to the try again page.

  16. kubrick said on January 6, 2020 at 3:43 pm

    Just wondering if this is a sign of intent for firefox desktop too.

    1. Iron Heart said on January 7, 2020 at 12:46 pm


      Most certainly. Mozilla has taken away user control over the browser for some time now. It’s not a new pattern.

  17. Yuliya said on January 6, 2020 at 3:25 pm

    Santa isn’t very kind towards mozillians this year, it seems they’ve all been naughty.

    1. Iron Heart said on January 7, 2020 at 12:56 pm


      Mozillians tend to be objectively stupid. Mozilla is funded by Google, Google is the one keeping this sinking ship afloat. Why? Because it’s better to have a weak and impotent “competitor” than to face antitrust charges due to being a monopoly. Same reason why Microsoft saved Apple from going bankrupt in the late 1990s, by the way. From Google’s perspective, them dominating the browser market with 90% market share and having a 10% market share “competitor” whom they financially control, would be optimal.

      But Mozillians act like they are heroic anti-Google fighters, the last resistance before the doom of the Internet. However, in order to be a true resistance, you have to be independent from the entity you are opposing. That’s just not the case with Mozilla. They get almost their entire income from Google, and they have followed virtually all Google proposals when it comes to new HTML standards, including heavy duty DRM. So much for “defenders of the free web”.

      Stupid is as stupid does.

      1. jern said on January 8, 2020 at 9:15 pm

        According to one website (https://www.w3schools.com/browsers/browsers_firefox.asp) Firefox was down to about 9.2% total usage in November 2019. It was in the mid-40% range in 2010.

        Chrome was at 81.3% in November 2019. It ranged from about 11-22% in 2010. Chrome v.1 was released 11 December, 2008

        I get the feeling that Mozilla/Google wants to reduce a user’s ability to control tracking. There is just too much money to be made tracking and identifying users.

        As for Mozillians being stupid…I think we all have blind spots. It’s hard to see how Firefox protects Google from antitrust claims when there are so many other browsers available.

      2. Iron Heart said on January 9, 2020 at 9:27 am


        Google funding Mozilla has more implications than just antitrust of course. Google also wants to be the default search engine of course, and I think you are on the right track regarding user-hostile changes on Mozilla’s part being influenced by Google.

        What we know is that Mozilla has followed virtually all Google proposals for new HTML features, including nefarious ones like DRM. When Mozilla made a last ditch attempt to break free from Google’s iron grip, namely when they signed the default search engine deal with Yahoo, it became evident that Yahoo’s market share did not(!) significantly increase due to that deal, meaning that most users switched the default engine back to Google immediately. One conclusion I draw from this is that being the default search engine is not the main intention behind Google’s money (because they can effectively achieve that goal without funding Mozilla). The main intention is to keep Mozilla afloat as a “competitor” and to influence them to implement nefarious code.

        I admit that I have used rather drastic wording in my comment, but you have to admit that the Mozillians acting like anti-Google fighters is amusing to say the least. Mozilla’s real position in the market is something they will likely never really grasp.

        That’s not to say that I think the market situation is optimal, far from it. However, I do realize that especially software markets tend to develop into monopolies (because third party developers usually do not develop for three or four different competitor platforms, for time and efficiency reasons), you can see this with Windows, Android, Chrome etc. I am also aware of the fact that the Mozilla management isn’t exactly known for sound decisions. Am I happy with the current situation? No, of course not, but pretending to be surprised about it would be a lie.

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