If you install Firefox and Thunderbird from Mozilla site, you have to create a symlink within '/usr/bin' to '(/wherever/extracted)/firefox/firefox' and '(/wherever/extracted)/thunderbird/thunderbird'.

To get LXDE-menu entries create within '/usr/share/applications' two new files "firefox.desktop" and "thunderbird.desktop"; have a look at "iceweasel.desktop" as an example, how to do it.

Greetings Werner * http://www.wp-schulz.de/knoppix/summary.html
Own Rescue-CD (Knoppix V6.7.1 remaster)