I was lucky to be in Riga when it was quiet, and had an eight bed dorm to myself for three nights. The hostel and the area it's in seem a little rough when you arrive, but the accommodation itself is lovely.
The hostel is between two tram stops, and building numbers are quite clearly labelled, so if you catch the number 7 tram from the city you'll see the sign for FireFighter on the side of the building, either from the tram or the street, depending on where you get off. As others have mentioned, reception isn't always open, so make sure you have a phone to call them to come and check you in (the number's on the door).
The room was clean, with a big window and lots of light and air, although trams do pass by regularly and the noise could disturb light sleepers. The adjoining bathroom was spotless, with great showers, and even a heated towel rail! The kitchen is small, with a microwave and toaster, and there's a fridge downstairs.
The wifi in the room was fast and reliable, and allowed me to book an extra night once I'd arrived and realised I wanted to stay a little longer.More