Firefox 4 is here as you might have already heard. I've noticed that not many people had updated their Firefox installations cause Firefox 4 won't be in official repositories until Ubuntu 11.04 Natty arrives. But fear not, "Mozilla Team" maintains Firefox Stable PPA for all of you waiting to update their favorite Firefox browser on Ubuntu 10.04 and 10.10. So here's the procedure for updating to Firefox 4.0:

sudo add-apt-repository ppa:mozillateam/firefox-stable
sudo apt-get update && sudo apt-get upgrade

Enjoy!