I was trying to install Firefox 3.0 in Mandriva 2006. I downloaded firefox-3.0.tar.bz2 and
using
#tar -jxvf firefox-3.0.tar.bz2
I unzipped.
When I give
# sh firefox
It shows that I require GTK+2.10 or greater. I Downloaded gtk+-2.12.10.tar.bz2
then
# tar -jxvf gtk+-2.12.10.tar.bz2
Then I ran ./configure
It showed the following error:

checking for BASE_DEPENDENCIES... configure: error: Package requirements (glib-2.0 >= 2.13.5 atk >= 1.9.0 pango >= 1.17.3 cairo >= 1.2.0) were not met:

Requested 'glib-2.0 >= 2.13.5' but version of GLib is 2.8.1

Consider adjusting the PKG_CONFIG_PATH environment variable if you
installed software in a non-standard prefix.

Alternatively, you may set the environment variables BASE_DEPENDENCIES_CFLAGS
and BASE_DEPENDENCIES_LIBS to avoid the need to call pkg-config.
See the pkg-config man page for more details.
checking for BASE_DEPENDENCIES... configure: error: Package requirements (glib-2.0 >= 2.13.5 atk >= 1.9.0 pango >= 1.17.3 cairo >= 1.2.0) were not met:

Requested 'glib-2.0 >= 2.13.5' but version of GLib is 2.8.1

Consider adjusting the PKG_CONFIG_PATH environment variable if you
installed software in a non-standard prefix.

Alternatively, you may set the environment variables BASE_DEPENDENCIES_CFLAGS
and BASE_DEPENDENCIES_LIBS to avoid the need to call pkg-config.
See the pkg-config man page for more details.

And then I downloaded glib, atk, pango, cairo. But I am a bit confused about installation and Setting PKG_CONFIG_PATH.
Please Help Me..

Usually the path for PKG_CONFIG_PATH is /usr/lib/pkgconfig.
Try setting the variable. You may reduce the dependency issues by setting up the variable.
But if packages are available through urpmi then that is a better option as all the packages will have their respective dependencies.

If you only just installed Mandriva-2006, I would suggest you install the latest version instead. If you want to run the latest programs on an old distribution, you will keep having trouble with outdated libs and such.