I'm travelling from Madrid to Brisbane, but I have a 9 hours layover at Dubai Airport. I do not plan to leave the airport, and the connection is with the same airline (Emirates). I'm from El Salvador.
Do I need a transit visa?
You do not need transit visa, however, do consider having one, as 9 hours is a long layover. Dubai airport is nice, you get free wifi and have plenty of window shopping opportunities plus restaurants but I would still consider getting out for that time and have a tour of the city whether it's day or evening time. Transit visas through Emirates website are around $60 and they process the visa within 3-4 working days.
When you are transitting within the same terminal 3 with Emirates then you do not require a visa as you won't pass through immigration.
And it seems this is the case for you.