Macbook - Text and video problem

Hi...

I just got my new macbook the other day and so far i've loved it. But i've had two problems with it.

1. Text lag, right now typing this (using firefox) the text seems to lag and doesn't always appear on the screen for a sec. I'm gonna try with other programs too incase it's firefox.

2. Last night watching videos on youtube it seemed to make the cpu temp go right up and the fans would come on until i stopped watching the video. Is there something different with youtube videos that make the cpu work harder than watching on quicktime for example?

Thanks.