Changing scrollbar for firefox & targeting two different frames from one button

I was wondering if you can change the default appearance of the scrollbar for firefox users.

As for my second question. This is what i’m trying to do. The layout of my website has 1 row (top) and 3 columns (left, middle, right). When i click a button (from the left frame), i want the top and middle frames to change at one time. I’m a newb at coding, so can you please post the code to help me understand.

Is there a limit on how long a code is for one page? As i’m copying and pasting over and over again the same code for a list of text, as i get farther and farther, the code starts to mess up and doesn’t work. Its very frustrating because i can’t get exactly what i have at the top of the page for the bottom.