But, yes the Firefox download manager is crap. It's ugly, buggy and useless. Just no way to turn it off...
btw, I don't know why that stupid download manager window has to pop up everytime I save an image from a page or anything else which is already downloaded. I suggested that the download manager window shouldn't appear if you're saving something that's already downloaded - this was from the 1.0 days - nearly a year went by and it's still exactly the same.