TIL; You can use any desktop Firefox addon in Firefox for Android by changing the user agent to Desktop Firefox and no need to create or have a collection.
To do this, first you need to have Firefox Nightly or Beta installed on your phone, then go to addons.mozilla.org and search in the search bar for User-Agent Switcher and install it by pressing the "Add to Firefox" button and now you should have User-Agent Switcher installed.
Now, you must press the 3 dots on the Firefox toolbar and go to Add-ons and open User-Agent Switcher.
Once there, choose Firefox 117 (or whatever version is available at the time you read this) and it doesn't matter if it's Windows or Linux, but to keep things simple choose Windows / Firefox 117.
Now, go to addons.mozilla.org again and again press the 3 dots and activate the option that says "Desktop site" and that's it, now you should be able to install any addon you want by going to the addon you want and pressing the "Add to Firefox" button, then you will get a pop-up asking if you want to add the addon and simply press yes.
I hope this guide is useful to someone! I recently came across this by chance and really found absolutely no information regarding this, so I posted it here.
It should be noted that not all extensions work as expected, some don't even open, but most of them work.
Interesting, I just read that they're opening beta testing of the ability to add all add-ons to Firefox Android again. I wonder if that's why this works, the support is already built into the beta/nightly versions of the app and changing your user agent just bypasses whatever checks they have to ensure you're enrolled in the beta test.
Maybe that's why you can't find any information about this and why it only works in the recent developer versions of the app.
I think the same, If it were not for the changes that Mozilla has been doing recently to bring more extensions to mobile devices, User-Agent Switcher could not be installed at all.
Are you sure it works on Firefox Beta? When I try to add the User-Agent Switcher, it just downloads the .xpi file and won't install it.
I really wish it would allow us to install .xpi files.
will try this when i have a chance.
could never quite get around to doing all the steps required to get extensions on ff mobile. it sucks because addons are one of the best features of ff desktop.
someone should just fork the extension "user agent switcher" and call it "enable addons for firefox mobile" or something. that way it will be findable to more people.
Unfortunately the add-on that I want, Yomichan, seems incompatible with Fennec. I've done all the collection steps, but I just get a generic "failed to install" message when trying to add it.
Edit: Holy crap. Switching the user agent totally worked. Dead simple. Thank you so much!
Why do they make this so complicated if the add-ons will just install?
Because it is not supported and they won't offer any help if it borks your device.
The add ons at the moment are developed & tested for desktop not mobile.
That's fine, add a big disclaimer that "here there be dragons" and a checkbox to accept that.
But they fight the user every step of the way to disable features that do in fact work.
I literally just created a new collection, but I'm saving this for future reference (though hopefully I won't need it if Firefox actually opens it up for add-ons as anticipated, a bit silly that we need these workarounds imo)
Does this work with installing xpi files from GitHub? (Say bypass paywalls for Firefox) I remember I used to be able to do this on Nightly, but suddenly I stopped having that ability
Nope. Side loading extensions doesn't work on Stable, Beta or Nightly.
Can confirm, it doesn't work.
You can install ublock origin on android mobile Firefox though, as that extension does work without OP's interesting work around.
Then to bypass paywalls all you have to do is add a custom filter list.