Buy OSRS Extended antifire(4)
The extended antifire(4) is a potion from Old School RuneScape. It comes with four doses. Each dose gives you full protection from dragonfire for six minutes. A full four dose potion gives you 24 minutes of protection in total. This makes it a strong choice for any fight against dragons.
The potion does have limits. It will not block Galvek's attacks. It will not stop the King Black Dragon's poison, shock, or freeze breath. Against Vorkath, it only blocks part of the damage. You must start the Dragon Slayer I quest before you can use this potion.
The game helps you keep track of your protection. A chat message warns you when the potion is about to expire. About 15 seconds later, a second message tells you it has worn off. This gives you time to drink another dose so you stay safe while you fight.
The potion is light too. It weighs only 0.02 kg, so it takes almost nothing away from the loot you can carry home.