This quest reward will give your pets permanent fire. Even when you logout or die the flame stays on them. Only arena removes it from the pet.
Found this exploit when i was lurking at wow-petopia and credits ofcourse to the guy who found it. So started looking for the quest and if it's still working. And yes at the moment it is still working. And you can use it on the pets that you tamed before who had a buff on them like my wolf there in the picture with oil stain buff. The fire buff does not remove the old buff.
https://i.imgur.com/4zOm3.png
The quest that you need is Choking the skies and it's located in Townlong Steppes. It's a chain quest you can't get this quest right away so i just went clearing the quest there a bit that led to the mantid. When you are on the quest Choking the skies. You will get a similar torch but it's not the same one for the exploit. It only works with the quest reward when you completed this quest.
You can also annoy hunters with it. Get in a bg and focus their pets to put them on fire.
Edit: If you are a hunter on EU and want your pet to be in flames. Send me a pm and we can crz and i can use my item on your pet to set it on fire. If you don't want to do the quest that is