A URL customization extension uses variables in bookmark. Define parameters name inside {{ }} in URL.
Custom Bookmarks allows you to use custom parameters in URL and re use bookmark for similar URL.
To define parameters use {{ }} in URL(s) while saving them .
For example, You're using ticketing system which has urls are like www.ticket.com/1 , www.ticket.com/2 etc. You can define URL in custom bookmark as www.ticket.com/{{Ticket}}. So you can open other tickets easily with providing only ticket number.