One of life’s current mysteries is how to edit Cinnamon’s menu system in Linux Mint Version 19 (Tara). The trick is either to run cinnamon-menu-editor in Terminal or navigate to Menu – Right-click – Configure – Menu – Open the menu editor. (Note the link at the bottom of the first section – Layout and content – of the window.)
Then the next question is how to remove one of the icons that are docked on the left side of the start menu. In my case, I have replaced Firefox with Opera so I don’t need the launch icon for Firefox in the top-left corner of the default start menu. While not intuitive, the solution is actually very simple – just drag the icon over top of the application menu and release it. The icon disappears. Magic!
References:
CINNAMON-MENU-EDITOR MAN PAGE
https://www.mankier.com/1/cinnamon-menu-editor
How to add a shortcut to a command to the Cinnamon menu?
https://askubuntu.com/questions/232053/how-to-add-a-shortcut-to-a-command-to-the-cinnamon-menu
How can I remove ‘docked’ items in the Cinnamon menu (“start”) bar on Linux Mint?
https://superuser.com/questions/516496/how-can-i-remove-docked-items-in-the-cinnamon-menu-start-bar-on-linux-mint?
linuxnorth.wordpress.com 
How to install??
Dietrich:
The editor should be installed with Linux Mint. Try right-clicking on Mint’s menu button (lower-left corner of the screen) and navigate to Configure – Menu – Open the menu editor.
Alan