Brake booster

[turbodiesel]

I was driving today, and came up on a stop light, the brakes felt weak like brake fading and they were pulling to the right. After I stopped I smelled brakes burning or brake fluid burning. I kept driving and they got better at the next light and kept getting better. I got home checked the fluid and it is full all the way to the top, but it appears some leaked out, can't really tell from where but there is quite a bit of brake fluid dripping from down the master cylinder from the resivoir. Brakes feel ok now but I am wondering what happened?? Brakes dragging? Fluid boiled over?? Leaky master cylinder?