I use 6# Fireline for almost all my beading. The only exception is when I put fringe on an amulet bag and want fluid movement of the fringe.
Many people complain that Fireline likes to knot and they get frustrated. At least some of the frustration is in misunderstanding what a knot is.
Fireline doesn't "knot", but it does kink and the kinks can get caught up in each other and you have what looks like a knot but really isn't.
The one thing you for sure don't want to do is tug on the mess from each end. All that will do is solidify the kinks and make them harder to open up.
You also don't want to start threading your needle through the mess in the hopes of undoing it.
So how do you deal with this mess? By preventing it from happening in the first place. Every time you exit some beads and before you pick up the next beads, run the length of the Fireline through your hand. The friction of running through your hand will create enough heat to straighten the Fireline.
Also when pulling the Fireline through your work, hold you fingers - the ones that aren't holding the work - so that the Fireline runs between them before it gets to the beads. This accomplishes two things. First, it will eliminate most kinks before they get to the beads and if there is a mess in the making, you'll catch it before it gets too close to your work.
If a mess happens - and we all get them - the first thing to do is stick your needle into a pin cushion and set the work down a distance away so that the mess is free between the needle and the work. Remember I said this is not a "knot" but just a bunch of kinks.
Examine the mess and you will see loops. The trick is to grasp a loop and gently push toward the "root" of the loop. You will see the loop back itself out through the mess and then you can go on to another loop. Usually it only takes a couple of loops to unravel the whole mess.