This is the 14566th most frequent German word.
liefernden
"Liefernden" means "delivering" or "supplying" (present participle of "liefern").
Here, 'liefernden' is an attributive present participle describing 'Firma', indicating the company is engaged in delivery.
Der fahrer der liefernden Firma war sehr pünktlich.
The driver of the delivering company was very punctual.
This usage of 'liefernden' functions to specify 'Elemente', portraying that these elements are involved in the act of delivery.
Die liefernden Elemente müssen vor der nächsten Produktion überprüft werden.
The delivering elements must be inspected before the next production.
In this sentence, 'liefernden' is again a present participle used attributively, describing the 'Personen' who are performing the delivery.