I did this mostly for the learning experience but it definitely works and doesn't erase any of your plugins. All comments are welcome, or even just let me know if you used it as im rather proud of myself. It should be future proof but then again i wont really know until a new version comes out.

For the install go and download the latest linux tar.gz HERE copy this script and save it to a text file named ff.sh ... make sure your tar is in the same directory and from bash do sh ff.sh

echo Type only the version number i.e. 3.0.10
read VER
tar -jxvf firefox-"$VER".tar.bz2
rm firefox-"$VER".tar.bz2
rm -r /usr/lib/firefox-3*
mv firefox /usr/lib/firefox-$VER
rm /usr/bin/firefox
cp /usr/lib/firefox-$VER/firefox /usr/bin/firefox
cat /usr/bin/firefox | sed "s|moz_libdir=/usr/local/lib/firefox-"$VER"|moz_libdir=/usr/lib/firefox-"$VER"|g" > /usr/bin/firefox1
rm /usr/bin/firefox
mv /usr/bin/firefox1 /usr/bin/firefox
rm /usr/bin/firefox-3.0
chmod 755 /usr/bin/firefox
Big thanks to archangel.amael as without him i wouldnt have known how to do this.