A large fir tree fell from the neighbors property over onto mine. The majority of the tree is now on my property (and has been for months now.. ) can I cut it up for firewood? It isn't part of my acreage that I actually use or even see very often but I could use the firewood & would like it cleaned up. I am willing to go talk to my neighbors about it before I start cutting it up but just wanted to find out what my " rights" were beforehand. Thank You

Your neighbor is responsible for removing it and paying for any damage if any.

As such, if he does not remove it, after being asked to. You have the right to remove it.

You go talk to him, and if he does not remove it, you can.

You have the right to trim any portion of a tree that is growing onto your property. But if we are talking about a tree that has fallen it is the neighbor's responsibility. I would do as Chuck suggested. Approach the neighbor and offer to cut up the tree and clean it up. If there was no damage to your property all the better. It would be nice to offer to share some of the firewood.

... can I cut it up for firewood? ...

Yes, you can.