If you are using a browser on Apple's OS X Lion - such as Safari or Google Chrome - the scroll bar does not always display automatically. Certain screens contain information that is only viewable by scrolling which is why you may want to change your OS settings to always display the scroll bar.
To display the scroll bar:
- Open System Preferences, either by clicking on the Apple menu or by browsing your Applications
- Select "General"
- In the "Show scroll bars" section select "Always"
- Refresh the webpage