Isn't Firefox 2.0 available in Ubuntu Dapper's repositories? If so, just use Synaptic or run the following command in the console :
sudo apt-get install firefox
If that doesn't work, then do a clean install...Edgy comes with Firefox 2.0.
BTW, you can install Automatix which will allow you to install the beta version of Adobe Flash Player 9.0 on Ubuntu (plus you can install other things...although technically it would be illegal to install some things such as mp3 codecs and DVD codecs.
Instructions:
If you want to upgrade from 6.06 LTS to 6.10, run the following command (either via ALT-F2 or a terminal):
gksu "update-manager -c"
The "-c" switch instructs Update Manager to look for upgrades at all. By default the 6.06 LTS release will not offer that automatically because of its long support cycle and high stability.
If you have a working network connection, it should then inform you about a new release and offer to upgrade your system.
As for Firefox - I use Swiftfox - you can download an Ubuntu version at www.getswiftfox.com.
Enjoy!
Regards, Ivan