Simple script to manually install Firefox to the /opt/ directory on GNU/Linux. Also handles updating. Primarily here for my own reference, use it if you'd like, I made it quickly so there are definitely things to improve. Requires wget. I recommend purging other Firefox installs beforehand. This script doesn't touch your profile directory.

firefox-get

#!/usr/bin/env bash
# Syd Lambert 2022, sydlambert.com

usage () {
    cut -c 5- <<EOF
    Usage:
        $(basename $0) command [options]

    A simple script for manual installation of Firefox to the /opt/ directory.

    Commands:
        install       Install Firefox
        status        See installation status, local & remote versions
        uninstall     Uninstall Firefox
        upgrade       Upgrade Firefox to latest version (if available)

    Options:
        -f, --force   Force & accept all prompts
EOF
}

# Get the latest Firefox version from mozilla.org, e.g. 108.0.1
version-remote () {
    curl -sfI 'https://download.mozilla.org/?product=firefox-latest&os=linux64&lang=en-US' | grep -Po '(?<=firefox-)[\d.]+(?=\.)'
}

# Get the current latest installed Firefox version (if present), e.g. 108.0.1
version-local () {
    readlink /opt/firefox | grep -Po '(?<=firefox-)[\d.]+'
}

# Determine if Firefox is already installed in /opt/
is-installed () {
    if [ -z "$(version-local)" ]; then
        false
    else
        true
    fi
}

# Remove temporary files
cleanup () {
    rm -rf /tmp/firefox-manager
}

# Prompt the user for a yes/no confirmation
yesno () {
    read -p "$1 [Y/n] "
    case $(echo "$REPLY" | tr '[A-Z]' '[a-z]') in
        y|yes) true ;;
        *) false ;;
    esac
}

# Install Firefox to the /opt/ directory. This will download the latest version
# from mozilla.org, extract it, then place it in /opt/. Firefox installations
# are versioned, new versions will coexist with old versions. This function
# sets up symlinks to relevant locations. The end result will look something
# like this after an install and an upgrade, for example:
#
#     Old version:                /opt/firefox-108.0/
#     Latest version:             /opt/firefox-108.0.1/
#     Symlink to current version: /opt/firefox/ -> /firefox-108.0.1/
#     Symlink to binary:          /usr/local/bin/firefox -> /opt/firefox/firefox
#     Desktop file:               /usr/local/share/applications/firefox.desktop
ff-install () {
    echo 'Downloading...'
    mkdir -p /tmp/firefox-manager
    wget 'https://download.mozilla.org/?product=firefox-latest-ssl&os=linux64&lang=en-GB' --trust-server-names -P /tmp/firefox-manager
    downloaded_version=$(find /tmp/firefox-manager/ -name 'firefox*' -type f | grep -Po '(?<=firefox-)[\d.]+(?=\.)')

    [ ! -f "/tmp/firefox-manager/firefox-$downloaded_version.tar.bz2" ] && { echo "Download failed."; cleanup; exit 2; }
    [ -d "/opt/firefox-$downloaded_version" ] && { echo "An installation of this version already exists."; cleanup; exit 2; }
    
    echo 'Extracting...'
    mkdir "/opt/firefox-$downloaded_version"
    tar -xjvf "/tmp/firefox-manager/firefox-$downloaded_version.tar.bz2" -C "/opt/firefox-$downloaded_version" --strip-components=1
    
    [ ! -d "/opt/firefox-$downloaded_version" ] && { echo "Extraction failed."; cleanup; exit 2; }
    
    echo 'Installing...'
    ln -fsn /opt/firefox-$downloaded_version /opt/firefox
    ln -fs /opt/firefox/firefox /usr/local/bin/firefox
    if [ ! -f /usr/local/share/applications/firefox.desktop ]; then
        mkdir -p /usr/local/share/applications
    wget https://raw.githubusercontent.com/mozilla/sumo-kb/main/install-firefox-linux/firefox.desktop -P /usr/local/share/applications
    fi
    
    cleanup
    echo 'Done.'
}

# See current installation status and latest version
ff-status () {
    if [ is-installed ]; then
        echo "Status:         Installed"
    echo "Version:        $(version-local)"
    else
        echo "Status:         Firefox is not installed"
        echo "Version:        N/A"
    fi
    echo "Latest version: $(version-remote)"
}

# Remove this manual install from the system (including desktop file)
ff-uninstall () {
    rm /usr/local/bin/firefox
    rm /opt/firefox
    rm -rf /opt/firefox-$(version-local)
    rm /usr/local/share/applications/firefox.desktop
}


[ -z "$1" ] && { usage; exit 1; }
subcommand=$1; shift
opts=$(getopt -o f -l force -n "$(basename $0)" -- "$@" )
eval set --$opts
while true; do
    case "$1" in
        -f|--force) opt_force="true"; shift ;;
        --) shift; break ;;
        *) usage; exit 1 ;;
    esac
done

case "$subcommand" in
    install)
        is-installed && { echo Firefox is already installed. ; exit 1; }
        [ "$(whoami)" != "root" ] && { echo "Please run this command as root." && exit 1; }
        if [ "$opt_force" != "true" ]; then
            yesno "Are you sure you want to install Firefox?" || exit 1
        fi

        ff-install
        ;;
    uninstall)
        [ ! is-installed ] && { echo Firefox is not installed. ; exit 1; }
        [ "$(whoami)" != "root" ] && { echo "Please run this command as root." && exit 1; }
        if [ "$opt_force" != "true" ]; then
            yesno "Are you sure you want to uninstall Firefox?" || exit 1
        fi

        ff-uninstall
        ;;
    upgrade)
        [ ! is-installed ] && { echo Firefox is not installed. ; exit 1; }

        this_version_local="$(version-local)"
        this_version_remote="$(version-remote)"
        echo "Local version:            $this_version_local"
        echo "Latest available version: $this_version_remote"
            [ "$this_version_local" = "$this_version_remote" ] && { echo "Already up-to-date."; exit 0; }
            [ "$(whoami)" != "root" ] && { echo "Please run this command as root." && exit 1; }
        if [ "$opt_force" != "true" ]; then
            { yesno "Would you like to upgrade?" || [ $opt_force ]; } || exit 1
        fi
        
        ff-install
        ;;
    status)
        ff-status
        ;;
    *)
        usage
    exit 1
    ;;
esac