messages scroll bar is too fast, it moves me 100s down not to next few. Can I change a setting to fix this?

I have a very frustrating problem. Its the sensitivity of the scroll bar when going down the messages list. If I click on it or try to move it down just as minute as possible... it moves me down hundreds of messages later. I need a way that I when I get to the bottom of whats diplayed in my window of messages listed, that I can continue down the listing. Its unusable as it is. I have to delete messages to move things up. I cannot find a setting. I am running Linux mint 17 Cinnamon as the OS. I would settle for a key programed to page down a few at a time.  ??? Ideals please. Right not, I just skip most of my email as its impossible to use inside of thunderbird as is.  :-(