a script that downloads a certain Firefox or Thunderbird version and installs it in an extra folder to create an independent and portable App for Linux. source: http://portableapps.com/node/16344

download-mozilla-portable.sh

#!/bin/sh
# Configure the following default variables according to your requirements
language="en-US" # e.g. "de" or "en-US"
if [ ! "$1" ]; then

	# default if no argument is set:
	version="95.0" # chose from http://download.cdn.mozilla.net/pub/mozilla.org/firefox/releases/
	application="firefox" # "thunderbird" or "firefox" but file extension, archive extraction, and binary
		
fi

if [ "$1" = "--help"  ] || [ "$1" = "-h"  ] ; then
	echo 'Usage: $0 [application] [version]'
	echo
	echo Usage:
	echo " for example"
	echo " $0 mozilla 68.5.0esr"
	echo ' -h --help 	display this help'
	exit 0
fi

if [ "$1" ] ; then
	application="$1"
fi

if [ "$2" ] ; then
	version="$2"
fi

echo result $0 $application $version

echo "This script downloads 
--
$application Version $version 
--
If you want to install another version press Ctrl+C and call this program with other options, for 
example: $0 $application 68.5.0esr"
echo

dir="$application-portable-$version"
if [ -d "$dir" ]; then
        echo "the folder $dir already exists, exiting"
        exit 0
fi

read -n1 -r -p "Press space to continue..." key

file="$application-$version.tar.bz2"
#for 32bit use the first line instead:
#url="http://download-origin.cdn.mozilla.net/pub/$application/releases/$version/linux-i686/$language/$file"
url="http://download-origin.cdn.mozilla.net/pub/$application/releases/$version/linux-x86_64/$language/$file"
# or example for firefox nightly:
#file=firefox-32.0a2.en-US.linux-i686.tar.bz2
#url=http://download.cdn.mozilla.net/pub/mozilla.org/firefox/nightly/latest-mozilla-aurora/$file

mkdir "$dir"
cd "$dir"
wget $url -O $file
echo "Extracting archive, please wait..."
tar xfj $file
rm $file
mv $application app
mkdir data

echo '#!/bin/sh' > "${application}-portable"
echo 'dir=${0%/*}' >> "${application}-portable"
echo 'if [ "$dir" = "$0" ]; then' >> "${application}-portable"
echo ' dir="."' >> "${application}-portable"
echo 'fi' >> "${application}-portable"
echo 'cd "$dir/app"' >> "${application}-portable"
echo './firefox --no-remote -profile ../data' >> "${application}-portable" 

chmod +x "$application-portable"
echo ... finished
cat <<EOM
... finished
"#close all running instances of another $application version:"
killall $application
"#change into the directory"
"# and start the application there"
cd "$dir"
./"$application-portable"
EOM

This is awesome!

One quick suggestion:
add echo 'user_pref("app.update.auto", false);' >> data/user.js; on line 58 to disable auto updates.

Thanks!

@sxiii I updated the gist with the new url