To Add libgtk-x11-2.0.so.0 in Ubuntu

I think the environment is a little different, but I will share the information for your reference.

Run Environment
Linux Mint 17 Qiana 32bit (equivalent to Ubuntu 14.04 Trusty Tahr)
KompoZer-0.8b3 (I got the kompozer, kompozer-data package below because I couldn't download it well with the addition of the PPA repository)

kompozer_0.8~b3.dfsg.1-0.1ubuntu2_i386.deb
kompozer-data_0.8 to b3.dfsg.1-0.1ubuntu2_all.deb

Verification Steps
Use the apt-file command to find out which package contains libgtk-x11-2.0.so.0 that is displayed as an error when running kompozer in the question. If you use the dpkg command, you can search only for installed files.Use the apt-file command to search for packages that have not yet been installed.

$sudo apt-get install apt-file
$ apt-file update
$ apt-file search libgtk-x11-2.0.so.0
libgtk 2.0-0: /usr/lib/i386-linux-gnu/libgtk-x11-2.0.so.0
libgtk 2.0-0: /usr/lib/i386-linux-gnu/libgtk-x11-2.0.so.0.2400.23
libgtk 2.0-0-dbg: /usr/lib/debug/usr/lib/i386-linux-gnu/libgtk-x11-2.0.so.0.2400.23

Now that I know it is included in the libgtk 2.0-0 package, I will install it.

$sudo apt-get install libgtk 2.0-0

Review the installed files.

$dpkg-L libgtk 2.0-0 | grep "so.0"
/usr/lib/i386-linux-gnu/libgdk-x11-2.0.so.0.2400.23
/usr/lib/i386-linux-gnu/libgtk-x11-2.0.so.0

Incidentally, libgtk 2.0-dev packages with dev are usually packages that summarize the header files (*.h) required for application development.
You need a shared library (*.so) to run the app, so you don't necessarily need a header file if you're just starting the app.