Hello there Cursor!!!
Welcome to LinuxQuestions.org. There're several ways of creating a shortcut. First, let's create a link from Mozilla executable to your /usr/bin, to keep things organized:
ln -s /usr/local/mozilla/mozilla /usr/bin/mozilla
Hint: not sure if you knew this already, but Linux has an auto-completition system, so just type a few characters, then TAB, it will complete the hole path/folder/file for you
. Remember also that you've to be root to perform those operations.
You should now be able to start mozilla from anywhere by simply typing mozilla at the terminal. Now, to create a shortcut to the desktop, it depends the desktop you are using. This example applies for KDE, but Gnome should be similar. Right click on an empty place of your desktop, then choose "Create new" >> "Link to Application". A window will open, fill the "General" tab with the application name, say, Mozilla. Then on the tab "Execute", theres a "Command" field. Simply write "mozilla" in there without the quotes.
Hint2: Linux is a case sensitive Operating System, unlike Windows, meaning that "mozilla" is different of "Mozilla", which is different of "MOZILLA".
Good luck mate!