Why can't I sign into YouTube?

Every time I try to sign into YouTube it’s been redirecting me to google and saying I need to have my cookies enabled. I am using the latest version of Firefox and my cookies ARE enabled. I even used custom settings and enabled the cookies in all ways. I have noticed my firefox has been speeding up a little, too. But I just can’t figure it out!?

Btw I can sign in to YouTube on IE but that browser is just too slow. What do I do for Firefox?