If you try to launch Firefox 3 on Debian Etch, you will see this message:
We're sorry, this application requires a version of the GTK+ library that is not installed on your computer.
You have GTK+ 2.8.
This application requires GTK+ 2.10 or newer.
Please upgrade your GTK+ library if you wish to use this application.
You need a GTK+ version of at least 2.10, which compiles fine on Etch.
Download GTK+ 2.10 from gtk.org and do this:
# cd /opt
# tar xjf gtk+-2.10.14.tar.bz2
# mkdir gtk210
# cd gtk+-2.10.14
# ./configure --prefix=/opt/gtk210
# make install
If .configure complains that some package is missing (mostly some devel stuff) install it and run .configure again.
Now create the start script "firefox.sh":