Head over to Steamfont, make sure to bring your trusty mining pick!
You want to get down to the area with the hot springs -670, 75, 1475 . You will find firesalt mines all over the area.
Once you have mined a single firesalt, you need to stand on top of a geyser and "use" the salt. If nothing happens, you are on the wrong geyser.
The geyser has been reported to be the steam vents -681, 79, 1482 in Steamfont Wetlands, not the larger geysers.
Once you have found the right one, you will spawn an air elemental mob that is a 70^^. Once he has spawned, he will attack, but you need to be sure to use the Jar of paste that Juna gave you on the cloak. This will coat the cloak with something to help hold the heat in. This paste must be on the cloak before the elemental dies or you won't get credit.
If you happen to die before you get your update, you will have to return to Juna and get another bottle of paste. Fortunately this elemental is only a ^^ and isn't overly difficult.
Once your paste is applied to your cloak, kill the elemental for your update.
Open the chest drop to receive the Heart of Jhal'Dolek. "Use" the heart on your cloak.
To repower the leather section of the Fourth Warrior's cloak I will need to find Jhal'Dolek. Juna says I can summon him by traveling to the Steamfont Mountains and finding the "Firesalt." In that region, I will need to seed the steam vents with Firesalt to summon Jhal'Dolek. Once summoned, I will need to coat the cloak with Juna's naptheric paste, allow the heat of Jhal'Dolek's gaze to ignite the cloak, and then soak the cloak in Jhal'Dolek's blood.
I need to travel to the Steamfont Mountains and summon Jhal'Dolek.
I need to seed the geysers of the Steamfont Mountains where Jhal'Dolek resided with Flamesalt.
I have summoned Jhal'Dolek.
I must approach Jhal'Dolek while the cloak is coated in naptheric paste.
My cloak is now engulfed in flames.
I must soak the cloak with Jhal'Dolek's blood.
I have repowered the leather cloak.
I should return to Juna.
I have spoken with Juna.
I have repowered the leather section of the cloak.
I have defeated Jhal'Dolek and coated the cloak in his blood, sealing the power of flame within the leather section of the cloak.