Why can't I use release/burst mode while in Lv (live view) on my Nikon D90?

I have a Nikon D90 with Tamron 18-200mm lens. The problem is that I can't use the release/burst mode while in live view… It only works when I take pictures while looking through the viewfinder. Why do you think that is and how can I fix it? Also, when I use live view I can't take pictures with it wanting to focus every single time… Shouldn't you be able to take pictures just by pressing the button and not have to wait for it to focus? I understand holding down the button half way to focus but if I want to take a picture without holding half way down first it won't let me.

I can't imagine why you would want to use the burst mode, let alone while holding the camera at arm's length.

Although the Nikon D90 was one of the first dSLR's to be able to auto-focus in the live view mode and the first dSLR with a video mode, all of the standard features used by photographers are still preferred when shooting still images.

The ultra-fast auto-focus is based upon using AF-S lenses and the auto-focus system built into the cameras viewfinder and lens. Live view uses a much slower contrast detection focus system.

More:

http://www.kenrockwell.com/...tom-af.htm

The camera works so that it it starts with the mirror up in live view, moves it down when one takes a button, moves it up again, takes the shot, and if i recall correctly moves it down and up again to get back into live view mode. So basically these are two mirror slaps instead of one for a shot taken in live view mode. Why that is so i do not know, perhaps the camera needs to take an additional light meter measurement with the mirror in the down position before taking a shot in live view.

Either way, as far as i know there's no way to use the full burst rate in live view mode.

If you do not want the camera to block the shot until it has focused, hold the AE-L/AF-L button when pressing the shutter release button.

"The problem is that I can't use the release/burst mode while in live view… It only works when I take pictures while looking through the viewfinder."

No, the problem it that you are trying to use a nice DSLR like a cheap point and shoot. Learn to use your DSLR like you're supposed to (using the viewfinder) or sell it and buy a point and shoot.