You can do this by changing a hidden preference.

1. Type about:config into the location bar and press enter
2. Accept the warning message that appears, you will be taken to a list of preferences
3. Locate the preference layout.scrollbar.side, then double click on it and change its value to 3

For more details on that preference see http://kb.mozillazine.org/Layout.scrollbar.side

There are also other things that need attention:

Your above posted system details show outdated plugin(s) with known security and stability risks that you should update.

1. Shockwave Flash 10.1 r85
2. Next Generation Java Plug-in 1.6.0_18 for Mozilla browsers

Update the Flash plugin to the latest version.

• http://www.adobe.com/software/flash/about/

Update the Java plugin to the latest version.

• http://www.oracle.com/technetwork/java/javase/downloads/index.html (Java Platform: Download JRE)