Sterilize jars and lids in hot water. Allow to dry and cool.
In a large copper pot or dutch oven, place peppers, vinegar, Fireshire, and sugar over high heat. Stir constantly until boiling.
Add pectin and salt. Simmer for 1 minute. Skim any foam off the top, and paddle jelly into jars using a funnel to carefully not make a mess on the sides of the jar.
Screw lids on tight and place into a large pot. Cover with water and bring to a boil to seal jars. Carefully remove jars from pot and allow to cool completely before storing.