Sterilize jars and lids according to safe canning practices.
Prepare the Strawberries: First wash berries and then remove the hulls. Crush the berries 1 cup at a time with a potato masher for the most uniform results. Do not use a blender, food processor, or hand blender. Crushing by hand yields the best results. Measure 5 cups of crushed berries and pour them into a large, non-aluminum pot.
Carefully measure the sugar in a separate bowl.
Stir the box of pectin into the crushed berries in the pot. Add butter to reduce foaming. Turn the stove to high and bring the berry and pectin mixture to a full rolling boil (a boil that doesn’t stop bubbling when stirred) while stirring constantly. Stir in the peppers, lemon juice, apple cider vinegar and the sugar. Return to a full rolling boil. Boil exactly 1 minute, while stirring constantly. Remove from heat.
Skim off any foam. Ladle jam into prepared jars, filling to within 1/8-inch of the top. Wipe jar rims and threads with a clean cloth or paper towel. Carefully place the flat lid on the glass rim. Then screw on the band. Place jars on elevated canner rack. Lower rack into canner. Water must cover jars by 1 to 2 inches; add more boiling water if needed. Cover and bring to a gentle boil. Process the jars for 10 minutes. Carefully remove the jars from the canner and sit them on a dishcloth on the counter. After jars cool, check seals by pressing the middle of the lid with your finger. If the lid springs back, the lid is not sealed and refrigeration is necessary.
Let jars stand at room temperature for 24 hours. Store unopened jars in a cool, dry, dark place for up to 1 year. Refrigerate open jars of jam for up to 3 weeks.