I'm just writing to confirm that the library IS in fact the place you need to go. (Which is in DM north, and you can get there by yourself, and hearth out)
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The trinket looks a lot like this:

+10 Fire Resistance
Equip: Restores 8 mana every 5 seconds.

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Mage Only&nbsp :-P

Keyllie, 60mage, Perenolde

Used the "blink through crack" technique to get my +FR trinket on my level 54 mage tonight. Tried about 10 times to get lined up correctly, then read a comment about using first person view.

Switched to the 1st person view and it worked the first time.&nbsp Thanks all for the advice.&nbsp :D

btw: 6600 xp at lvl 54

How to get to the Library if you are a mage (no key required)

1. Enter DM and head to the North portal entrance.

2. GET NAKED! Pull a mob and get killed.

3. Walk back to your corpse, but DO NOT REZ.&nbsp While you are a ghost, walk through the locked door and rez between the locked door and the portal itself.

4. Enter instance.

5. Wait for the single patrolling mob to walk out of aggro range to the right.

6. Run straight across the "hall", hug the wall, and onto the ramp.

7. Running at an angle, jump up onto the raised edge of the ramp.

8. Drop down off the edge of the ramp in the grass area (try to land on the raised edge that runs along the outer walls of the grass area).

9. Get as close to the next ramp as you can without getting aggro and blink forward onto the second ramp.&nbsp If you are 60, you can simply walk to the ramp, just be careful.

10. Walk down the ramp, switch to the "first person" camera view.

11. Line yourself up so you can see THROUGH the crack.

12. Blink (you should suddenly be on the other side of the door, inside the hallway leading to the library)

13. No mobs from here, so just walk down the hall into the library (which is filled with "friendly' NPCs), turn in quest, get your trinket, dance a happy jig, hearth out.

Yes, you do have to die once to get through the first locked door, but if you get naked before you draw aggro, you take no durability loss and hence no repair bill...&nbsp no paying someone to unlock the doors either.

Its actually quite funny to se what people write about this trinket.

The people who doesnt like it, are obviously people who has'nt been to Molten Core yet.

Tanks in MC and Onyxia's Lair should have at least 150 Fire Resistance, and best with 300.
Not so much for Lucifron and the other "small" boss's, but for Majordomo and especially Ragnaros.

The 150 Fire Resistance goes for spell casters as well, Ragnaros bursts out a fire wave that does 6000 damage (If i remember correctly) AND knocks you back, so you end up in lava.
Both the damage and the knockback can be resisted fully or to some extent, the higher resistance you have.

So yes, this book IS worth the while.