Chapter 6: Hunting the Firehawk - Borderlands 2
Head to the second floor and open the safe. You can now store items here for later use. You need to head to Frostburn Canyon but before heading there, there are new optional missions available again. You can opt to do them first before completing this story mission.
Do No Harm – Zed
Medical Mystery - Zed
Claptrap's Secret Stash – Claptrap
No Vacancy – Echo recorder in Happy Pig Motel
Neither Rain nor Sleet no Skags – Happy Pig Motel board, after completing "No Vacancy"
When ready, fast-travel to the Three Horns – Divide. Head to the marker, which you can access by jumping off the ramp using your vehicle. Find the camp there and clear it out of enemies. Enter the canyon afterward.
Make your way inside and fight off a few enemies. Don't bring entirely fire-based weapons here as there are heavily armored pyro nomads and later on, fire spiderants in the area as well. Just clear the immediate areas and follow the next markers until you reach the trap-filled passage leading to the Firehawk's lair.
Approach the lair for a short scene. Revive Lilith then retrieve the eridium and give it to her. Once done, you have to repel several bandit attack waves. She'll be assisting you with her phasewalk abilities but you have to do most of the job. The final wave will include two badass bandits. Just concentrate on one of them and keep moving to avoid getting pummeled by their heavy attacks.
After repelling the enemy attack, get another eridium and hand it over to Lilith so she can recover her strength. Talk to her again to turn over the quest. You can head back to Sanctuary for more optional missions.