user.js | Firefox Fenix Nightly, Iceraven, Fennec F-Droid or Icecatmobile

The user.js file is used to configure Firefox for android in the safest and fastest way possible. There are 2 versions:

Default user.js for average users.
Another one with less connections as possible, meaning there are not automatic addons updates. You'll have to uninstall and reinstall them (not recommended)

Goals:

This user.js has been designed for mobile purposes and you can use it on these browsers:

I would like to suggest the use of Amaze or TWRP File Manager before proceed.

Download and install Firefox Fenix Nightly, Iceraven, Fennec F-Droid or Icecatmobile from their official websites (see above)
Start the browser for the first time (offline mode/no data connections) and wait about 5 sec.
Close it.
Clone or download zip file and extract it
Locate browser's installation directory similar to this:

✳️ Firefox Fenix Nightly data/data/org.mozilla.fenix/files/mozilla/[xxxxxxx].default

✳️ Iceraven data/data/io.github.forkmaintainers.iceraven/files/mozilla/[xxxxxxx].default

✳️ Fennec F-Droid data/data/org.fdroid.froid/files/mozilla/[xxxxxxx].default

✳️ Icecatmobile data/data/org.gnu.icecat/files/mozilla/[xxxxxxx].default
Copy the extracted user.js file to the above installation directory.
Delete prefs.js file inside the above directory
Start the browser and test if user.js was applied : browse to about:config (put it in search bar) and look if config.applied is true.

If this doesn't work I suggest you to use the ROOT METHOD 2 below.

Download and install the browser from their official websites.
Download and install User.js Updater
Start the browser for the first time (offline mode/no data connections) and wait about 5 sec.
Close it.
Open User.js Updater app and grant storage permission.
Choose Custom and write the following:

https://git.nixnet.xyz/Narsil/mobile_user.js/src/branch/master/user.js
Tap UPDATE at the bottom and grant root permission.
Start the browser and test if user.js was applied : browse to about:config (put it in search bar) and look if config.applied is true.
AFWall+ USERS: You can disable Use Download Manager option into Settings and enable data connection just to the app itself.

I really thank the following authors:

[Quindecim] (https://git.lelux.fi/quindecim/mobile_user.js) - Without him, this project could not be possible.
[Arkenfox] (https://github.com/arkenfox/user.js) - Updates.
[v1nc] (https://github.com/v1nc/) - For his user.js updater app

GNU General Public License v3.0.

See LICENSE for more details.