Need to identify small indoor fir tree?

I have a small fir tree indoors--about 2 1/2 feet tall. I can't seem to identify what exactly it is, which I need to do in order to take care of it. The lower branches keep browning and drying out. I trim them off and it seems fine and perky for a while. Then a month later, the lower limbs brown and dry up again. Any ideas of web sites to visit? I have googled and don't find anything about indoor pines or firs except stuff on bonsai, etc... which this is nothing like.