Using firefox 3.5 as a defult browser over 3.0.11

If would be nice if you would always give the ubuntu release that you're using. ;)

but anyway - you might be interested in the ppa of the mozilla daily build team on

https://edge.launchpad.net/~ubuntu-mozilla-daily/+archive/ppa

I don't know if the firefox version in ubuntu get's replaced if you use it (didn't test it since I can't risk loosing 3.0) but if not, it should be as easy as replacing the 'firefox' symlink in /usr/bin to your firefox version. Here it looks like this:
0 lrwxrwxrwx 1 root root 11 2009-06-13 21:17 /usr/bin/firefox -> firefox-3.0

good luck !

There is a firefox-3.5 PPA that will probably be easier to use. Try the following directions:

1) Open a terminal (Applications->Accessories->Terminal).
2) Type this command and press <Enter>: sudo gedit /etc/apt/sources.list
3) Add the following lines to the bottom of the file:

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

4) Press save.
5) Run the following command in the terminal:

 sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-key 247510BE

6) Run the following command in the terminal:

sudo apt-get update && sudo apt-get install firefox-3.5

7) To set firefox-3.5 has the default browser, do the following:

a) Open System->Preferences->Preferred Applications
b) Change Browser to "Custom"
c) Change the command to: firefox-3.5 %s
d) Press Close

I hope this helps.

Firefox 3.5 wont be the default browser until Karmic Koala (i guess) so you are not going to find it or any updates for it in Synaptic.
To install it or have updates, you will have to add the PPA for Ubuntu Mozilla Daily Build Team
https://launchpad.net/~ubuntu-mozilla-daily/+archive/ppa

You have some instructions about how to do it here: https://launchpad.net/+help/soyuz/ppa-sources-list.html

Open a Terminal: Applications - Accesories - Terminal
Then Add the next to entries to your sources.list

sudo gedit /etc/apt/sources.listt

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

Then add the Key

    sudo apt-key adv –keyserver keyserver.ubuntu.com –recv-keys 247510BE

    sudo apt-get update

    sudo apt-get install firefox-3.5

Thats it. Hope that helps.

Ups, sorry Steven.;-))
Much better your description.