Ubuntu tutorial: How to install Firefox 3.5
A lot of people are searching for it so I thought I can write a how-to for installing Firefox 3.5 on Ubuntu 9.04 Jaunty Jackalope.
1) First of all you need to add the mozilla-daily repository:
sudo gedit /etc/apt/sources.list
and append at the end of the list:
deb http://ppa.launchpad.net/ubuntu-mozilla-daily/ppa/ubuntu jaunty main
save and close the file.
2) Now add the key:
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 247510BE
3) Update
sudo apt-get update
The "True" Firefox 
4) Install
sudo apt-get install firefox-3.5 firefox-3.5-gnome-support
5) Replace symbolic links
At this point you can run firefox 3.5 just by typing firefox-3.5 in the command line. But if you’re sure you don’t want to use firefox 3.0 anymore go to /usr/bin/ and remove the symbolic link:
rm -r firefox
and make it point to firefox-3.5
ln -s firefox-3.5 firefox
The Firefox-3.5 codename on Ubuntu is Shiretoko so don’t be suprised when you see your browser is named Shiretoko. That’s all, hope it helps feel free to comment .
