Perhaps you have some misunderstanding. Only shell scripts use terminal commands. Programs like Firefox and such might have a shell script to install or to start, but the main program will be an executable, consisting of binary computer code. The program makes system calls to the kernel for doing things like opening files. Those are not terminal commands. If you want to see what system calls a program make, you can use the strace program for that. But I'm thinking this is not what you want.
Going back to Firefox, you can find what the name of the file is that is run when you start it from the menu by installing Alacarte (on Gnome; on other desktop environments you will using something else). Alacarte allows you to see which command is run. For Firefox the command is "firefox %u". To find out more, I hop to the terminal and do the following:
vincent@katya ~ $ which firefox
vincent@katya ~ $ file /usr/bin/firefox
/usr/bin/firefox: symbolic link to `../lib/firefox-11.0/firefox.sh'
vincent@katya ~ $ man file
vincent@katya ~ $ file --dereference /usr/bin/firefox
/usr/bin/firefox: POSIX shell script text executable
vincent@katya ~ $ cat /usr/bin/firefox
<contents of the file is shown here, cut for brevity>
I first use the command "which" to find where "firefox" is. Then I use the command "file" to get information about the file. It shows me the firefox file is a symbolic link to some other file. So you see me consulting the manpage for file to find out how I have it follow symbolic links
Next I run it properly and it tells me firefox is a shell script. So it contains terminal commands
Next I output the contents of the file. You could have done "gedit /usr/bin/firefox" instead to show the contents of the file in a nice editor.
Here is a topic with links to tutorials and documentation on terminal commands: viewtopic.php?f=213&t=77062