Sorry, I thought is is a little hard, but it was so easy :) - for LiberKey 5.
For example, I'll show how to do "Firefox -safe-mode" (creating a shortcut for it).
Go to LiberKey menu, to the category where you shortcut is (e.g. Browser).
To maintain original shortcut, copy and paste the shortcut of the app you want to add parameters. Put in another category, if you want. (e.g. copy and paste Firefox shortcut, and drag and drop it to My Menu).
Mouse right click on new shortcut and choose "shortcut properties". Note: if you choose "app properties", changes will affect all shortcuts for that app, so it is better to change a shortcut properties if you want to maintain original shortcuts.
In shortcut tab, change the name to something that remember you about the parameters you use (e.g. Firefox Safe Mode).
In advanced tab, change parameters field to what you want (e.g. -safe-mode)