I have installed gos 3.1 and I want to upgrade thunderbird

If you add the mozilla ppa you can get the daily build.

This is what I did:
sudo add-apt-repository ppa:ubuntu-mozilla-daily/ppa
sudo apt-get update
sudo apt-get upgrade

And it did not do it.

This is what it says:
cevin@cevin-desktop:~$ sudo add-apt-repository ppa:ubuntu-mozilla-daily/ppa
[sudo] password for cevin:
sudo: add-apt-repository: command not found
cevin@cevin-desktop:~$

sudo apt-get install python-software-properties

With some websearching you could have found that out....

This is what it said:

cevin@cevin-desktop:~$ sudo apt-get install python-software-properties
[sudo] password for cevin:
Reading package lists... Done
Building dependency tree
Reading state information... Done
python-software-properties is already the newest version.
The following packages were automatically installed and are no longer required:
  linux-headers-2.6.24-19-generic xulrunner-1.9.2 libqt4-core
  xulrunner-1.9-dom-inspector libqt4-gui libxul0d libmozjs0d libxul-common
  linux-headers-2.6.24-19
Use 'apt-get autoremove' to remove them.
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.

You can clean that up with:

sudo apt-get --purge autoremove

Ok we'll do it the old skool way:

gksudo gedit /etc/apt/sources.list

add these 2 lines to the bottom of the file:

deb http://ppa.launchpad.net/ubuntu-mozilla-daily/ppa/ubuntu lucid main
deb-src http://ppa.launchpad.net/ubuntu-mozilla-daily/ppa/ubuntu lucid main

Save the new file, close gedit and run:

sudo apt-get update

You WILL get an error about GPG keys, if use this code:

sudo apt-key adv --recv-key --keyserver keyserver.ubuntu.com XXXXXXXXXXXXXXXXX

but replace XXXXXXXXXXXXXXXXX with the hexadecimal code you are presented with, it will import the key for you. If you rerun:

sudo apt-get update

It should then be smooth and you can install the dily builds of firefox (even firefox 4) if you like mozillas bloated browsers. or the beta releases of thunderbird, codenamed "shredder"

Enjoy

I upgraded to 10.10