I mostly followed Ubuntu Geek’ instructions.
I made the backup of the profile directory:
sudo cp -R ~/.mozilla ~/.mozillabackup
I checked in Synpatic package manager and found that libstdc++5 was already installed.
I followed the link they provided for downloading the new version.
I extracted it as they suggested to the /opt directory:
sudo tar -C /opt -jxvf firefox-3.0b3.tar.bz2
For the plugins, I created the link that they suggested. Make sure you see that you have the right plugins directory — it looked like there could be various locations for the plugins.
sudo ln -s /usr/lib/firefox/plugins/* .
I found some information about controlling profiles, and so, I created a different profile for Firefox3. First, I created a copy for Firefox:
cp -r .mozilla .firefox3
/opt/firefox/firefox -P “firefox3″
The first time, it brought up the “Choose User Profile” dialog. So, I clicked on the Create Profile button and created a new profile by the name of firefox3. For the path, I chose $HOME/.firefox3/firefox/tgvjuj9r.default (the copy of my default profile).