Firefox version starter

#!/usr/bin/env bash

PROFILE=$(mktemp -d)

if [[ -d ~/firefox/default/ ]]; then
    cp --recursive ~/firefox/default/* $PROFILE
fi

if [[ $# -eq 0 ]] ; then
    if [[ -x /usr/bin/firefox ]]; then
        echo 'Launching...'
        /usr/bin/firefox --new-instance --profile $PROFILE
        rm -rf $PROFILE
        exit
    else
        echo "No version given and no installed version found"
        exit 1
    fi
fi

# if the given version is without minor version (e.g. "55" instead of )
VERSION="$1"
if [[ ! -z "${VERSION##*.*}" ]]; then
    VERSION="$1.0"
fi

# if the version has already been downloaded, then we can launch it and be done
if [[ -x ~/firefox/firefox-$VERSION/firefox/firefox ]]; then
    echo 'Launching...'
    ~/firefox/firefox-$VERSION/firefox/firefox --new-instance --profile $PROFILE
    rm -rf $PROFILE
    exit 0
fi

mkdir -p ~/firefox/firefox-$VERSION/

# download the version from mozillas archive
echo 'Downloading from archives...'
wget -q \
    -O ~/firefox/firefox-$VERSION.tar.bz2 \
    http://ftp.mozilla.org/pub/firefox/releases/$VERSION/linux-$(uname -m)/en-US/firefox-$VERSION.tar.bz2

# if the download failed, clean up and die
if [[ $? -ne 0 ]]; then
    echo 'Download failed (possibly unknown version). Cleaning up...'
    echo 'Available releases: http://ftp.mozilla.org/pub/firefox/releases/'
    rm ~/firefox/firefox-$VERSION.tar.bz2
    rmdir ~/firefox/firefox-$VERSION/
    exit 1
fi

# unpack the tar
echo 'Unpacking...'
tar -xjf ~/firefox/firefox-$VERSION.tar.bz2 -C ~/firefox/firefox-$VERSION/ >/dev/null
rm ~/firefox/firefox-$VERSION.tar.bz2

# disable auto update mechanism (the hard way)
rm ~/firefox/firefox-$VERSION/firefox/updater
rm ~/firefox/firefox-$VERSION/firefox/updater.ini
rm ~/firefox/firefox-$VERSION/firefox/update-settings.ini

# and we're done
echo 'Launching...'
~/firefox/firefox-$VERSION/firefox/firefox --new-instance --profile $PROFILE
rm -rf $PROFILE