A side remark in this recent add-ons blogpost: Introducing a scalable add-ons blocklist - Mozilla Add-ons Community Blog may shed some light on the factors involved with allowing the installation of arbitrary extensions on Android:
We are currently evaluating additional optimizations in order to further minimize the size of the blocklist for use on Fenix, the next major release of Firefox for Android.
This may of course also not have been a factor in the decision.
just gonna post the add-ons i use in fennec:
fenix really shouldnāt have been released in this state 
add-ons are the only reason i use firefox on my phone. Some add-ons should really be built-in.
Iām not letting my Firefox on Android to update until you start allowing all extensions again. If it updates itself, the decision is rather clear: uninstall and switch to Kiwi or Brave.
Workaround - install Fennec via F-Droid - it is a fork of Firefox before they broke add-ons:
https://f-droid.org/en/packages/org.mozilla.fennec_fdroid/
Iāll use Fennec F-Droid until Mozilla comes to it senses. Iāve lost all my passwords during upgrade anywayā¦
So Long, and Thanks for All the Fish
In the meantime, you can add the āI donāt care about cookiesā blocklist to uBlock Origin in the Firefox.
Go to uBlock Originās settings, tap on the dashboard, then visit the filter list tab, scroll to the bottom, and import a custom URL.
The blocklist URL is https://www.i-dont-care-about-cookies.eu/abp/
It is quite a few more steps to set it up, but youāll have a similar cookie reduced experience when done.
I used Firefox because it supported extensions. Not because it shipped with a tiny curated list of guaranteed-foolproof extensions, but because it supported extensions, period.
I donāt think there has been a good reason other than its broad general support of all extensions for anyone to use Firefox, for quite some time. The 2017 extensions fiasco was embarrassing and bad news already, but the new, improved fiasco of 2020 is so far looking less like a setback and more like the end of Firefox.
Other browsers on Android now support extensions. They arenāt as polished-looking, but they mostly work. Firefox doesnāt mostly work, because Firefox has decided to drop the one feature that really set it apart. New little features can be nice, but not at the cost of dropping the main feature.
I suspect that this has happened under pressure from āour partnersā who donāt enjoy the possibility that their āservicesā might be circumvented.
Fennec on f-droid is the answer for now until Firefox reverts this or another fork replaces Firefox entirely.
All versions of Fennec, including the last - 68.11.0 - are still available from Mozillaās download site, btw. (Iāll not post the url - itāll probably change - but itās easy to find.) Iāve put the APK on my devices in case they accidentally update.
āKim Cosmosā makes an interesting point in a comment elsewhere. Iāll quote part if it:
The real reason for the addons problem was that when developers submit an addon they can choose which platform it runs on, OR check the āallā box. Because firefox crowed cross compatability the developers always ticked āallā despite android FF having no toolbar for launching these addons. The developers were assuming FF would check, FF assumed the developers would check. Consequently about 2/3 of all the android addons never worked.
Thatās certainly true. Because it was so hard to find real Android addons on AMO I added āAndroidā to the title of some of my addons.
The piece, by Vladimir Palant, is here: A grim outlook on the future of browser add-ons | Almost Secure
Of course itās only a solution for nerdy people, not for the ānormalā ones.
And when does Fennec implement the recent update which killed the FF?
This is the way Iām seeing things a couple days after the loss of most my add-ons (user, not maker):
Yeah, fenix is faster and smoother. Would love to use it.
Until I cannot install arbitrary add-ons that will never get enough ālikesā to be vetted and added by Mozilla I have switched to F-Droid Fennec (Firefox Sync works by the way!). This is a temporary solution and if I donāt see Mozilla coming to itās senses, I will find a modern Browser that does what I want.
It doesnāt really matter which add-ons Iām missing, itās about diversity and control.
How do you plan on newly developed Add-Ons ever making it to a recommeded status? All things start small, none of the Add-Ons that are Recommended, werde noticed by the Mozilla Staff from day one. The beauty of add-ons is that they do not require an active interest by the browser-maker, just of the author and those who what to use them.
@Mozilla_Support I would really love some input here (or are you busy coding the unlimited add-on support, which is the only acceptable reason for your silence?).
Kiwi is not great in all ways, but itās better than Firefox.
Not even just one of many others. Firefox has become a pointless choice, when it was formerly a viable choice. To make a game analogy, Firefox was a lackluster player who had one very powerful secret weapon, powerful enough to win frequently. Since the switchover, Firefox is a lackluster player, period.
The out-of-control extension free-for-all was and still is everything that Firefox has going for it.
@d-r-k Youāre right, of course. The objective should not be to allow sideloading but to allow addons from AMO. But sideloading in the nightly build (which is pre-beta) is a good first step.
It seems that the approved addons are part of a ācollectionā on AMO. During migration any addon not in this collection is relegated to a ānot supportedā bucket. The obvious way forward is to allow addons that are known to work and are assessed as harmless to be put in another collection - āunapprovedā. Users would have to opt in to this collection.
Getting an addon like mine into this new collection could involve two steps:
1 That the author has tested in nightly. Mozilla could monitor that with telemetry. (That would solve the problem Kim Cosmos identified.)
2 Maybe a stricter automatic validation tool, depending on the addonās permissions. Addons such as mine, which are mainly content scripts options and local storage, are very low risk.
But what Iād really like now is a commitment to enable addons from AMO eventually. Or at least something more positive than the vague marketing-speak weāve had for months. Then Iāll just carry on using 68 and wait. (The early Maemo builds lacked a few features too!)
And some sign that the Fenix team are reading this?
Hey folks, we recently published an update about extension support in Fenix.
The three main takeaways are:
Excellent news indeed. Thanks
Hi Caitlin,
thanks for the heads-up about the post.
I appreciate that the subject is on your radar, but the proposed measures are simply insufficient.
Some of the Addons I use have 200 users, they will never ever make it onto some Recommended Extensions list. It is THIS kind of customisability that made FF attractive. Not a list of Extensions that might as well be part of the bowser itself.
Pushing me to use an alpha-version of the browser in order to be able to use the addons I want is not fair. Just give me about:config back, let me set some setting to true, show me a warning that I am doing this at my own risk and let me install any addon I want.
What is so damn hard about that?
Firstly, I agree with @imforumman ā a user should not be forced into using the alpha of the browser just to use an uncommon addon. Consider the example of a corporate environment where a certain addon is needed, but which isnāt a recommended addon. It would be untenable for that use-case to use the Nightly version as it is simply too unstable for production use.
But also, only allowing for addons to be installed from AMO isnāt sufficient. What if a developer wants to test the addons before uploading to AMO? Just like on desktop, one needs to be able to test an arbitrary XPI without it coming from AMO.
This applies also for in-house extensions, or other extensions which donāt belong on AMO in the first place. Mozilla should definitely not impose a walled garden on nightly users (nor on release users, for that matter!).
Firefox already shot itself in the foot by permanently disabling a lot of the best extensions a few years ago. Now the gun is aimed at the head; hoping they put the gun away instead. Difficult maintainability is peanuts, compared to being out of work with nothing to maintain. (Thatās if maintainability was ever the issue, rather than disapproval from corporate sponsors.)