Ok. Let’s get this matter sorted out.
The latest official Firefox release is version 92 as per their release notes. It was released on Sept. 7, 2021.
Now, check out the output from a pacman query below. This is the package I got installed from the Unstable repository.
~ >>> pacman -Qi firefox
Name : firefox
Version : 92.0-1
Description : Standalone web browser from mozilla.org
Architecture : x86_64
URL : https://www.mozilla.org/firefox/
Licenses : MPL GPL LGPL
Groups : None
Provides : None
Depends On : gtk3 libxt mime-types dbus-glib ffmpeg nss ttf-font libpulse
Optional Deps : networkmanager: Location detection via available WiFi networks [installed]
libnotify: Notification integration [installed]
pulseaudio: Audio support [installed]
speech-dispatcher: Text-to-Speech [installed]
hunspell-en_US: Spell checking, American English
xdg-desktop-portal: Screensharing with Wayland [installed]
Required By : None
Optional For : None
Conflicts With : None
Replaces : None
Installed Size : 222.90 MiB
Packager : Jan Alexander Steffens (heftig) <heftig@archlinux.org>
Build Date : Tue 07 Sep 2021 10:02:01 PM CDT
Install Date : Wed 08 Sep 2021 09:29:32 PM CDT
Install Reason : Explicitly installed
Install Script : No
Validated By : Signature
For the repositories in the other branches, check out the link on @nickgnomic’s post above. I will not repeat it myself.
From the output above, you can infer the maintainer (actually an Arch Linux maintainer) built the latest package the same day the source code was officially released.
As a conclusion, if you don’t like to wait, probably the way to go is setting up your package management to the Unstable branch (@Wollie already gave you a hint on how to do this).
Otherwise, the package will go through the Manjaro usual life cycle. (@nikgnomic already posted a link with a handy flow diagram above)
Please note that if you join the unstable branch, you are expected to help others by testing packages, reporting issues and providing fixes so other may benefit from your feedback.
If you prefer to install it from source, that’s your choice and most likely you will be on your own.
This should clear up your question and as such, I’ll go ahead closing this thread.