Flash in website prevent keystrokes...

I don't know why this happens, but if a website has flash, I can't use keystrokes to control my browser. I'm currently using FireFox 3.x, It's been like this forever, so I don't think it's the browser version that's the issue. If you're on youtube, for example, and have the video playing, try to use the Alt-D, to access the address bar. You can't.. seems that flash is responding to your keystrokes. That's something I don't like at all. I want keystrokes to be browser specific only!