It's a little tricky if you are running a 64-bit OS which most people will be.
The weird thing is that the Seamonkey website for Linux seems to only provide a 32-bit download.
First unpack it
tar -jxvf seamonkey-2.49.2.tar.bz2
Try to run it
XPCOMGlueLoad error for file /home/queenlazina/Downloads/seamonkey/libmozgtk.so:
libgtk-3.so.0: cannot open shared object file: No such file or directory
Couldn't load XPCOM.
Seems that libgtk is installed:
But note it is 64-bit and you need the 32-bit library since Seamonkey is 32-bit.
We need to enable i386/32-bit architecture and add the libgtk for 32 bit
sudo dpkg --add-architecture i386
sudo apt-get install libgtk-3-0:i386
After that you can run Seamonkey finally!