. If you already know it, just go to Tools > Avant Browser options > Add-ons > Add-ons tab > Add > enter a title, and paste a command. If you're going to write in that window, instead of paste, you need to use Shift/Ctrl + Enter to make new lines. Select either a button script, or an auto-execute script for your addon. Button scripts require an icon. Auto-execute scripts have a bug, that when you refresh the current page, they are not executed.