I've used FireLine a lot and braid a little on spinning reels, and I've a couple of observations to add. First, you will need to wind on a little monofilament onto the spool first to keep your line from slipping on the spool. This assumes that your reel doesn't have one of those little rigging slots where you can thread your line through and tie a solid knot. The second thing is to not overload your reel with either FireLine or braids. I have fewer tangles with a slightly underfilled spool. My observations are from using the stuff for bass fishing and not steelheading.

And Mooch was right on the money with the uni-knot. The uni to uni splice is the best way I know to join superlines to monofilament.

Keith