Default Folder X has a pernicious problem whereby the background process, Default Folder X BG, uses more and more processor cycles the more you use it. This processor load is present even when you are not using DF. It's like a memory leak only with processor cycles. Check it out using Activity Monitor. When you first launch DF, it's well-behaved, showing 0.00 % CPU. But as you use it, for me typically a few days, that CPU usage creeps higher and higher until it is 3% or 5%. Quitting the program and restarting it starts the ramping-up process over at 0% again. I don't know how high it actually might go. I've communicated with the developers--they have been interested but have not been able to fix the problem.