I have installed Internet Download Manager. I noticed that on IE, to download videos, the file format is mp4 but not mkv, which I guess is correct as Youtube doesn't provide mkv. But on google chrome, IDM shows file format mkv & no mp4. And Firefox - mp4, no mkv. So IE - mp4 & GC - mkv & FF - mp4 Why no mkv in IE & mp4 on GC & mkv on FF?