A theme is a type of Firefox add-on which changes the visual appearance of Firefox. This document describes how to find, install and manage themes in Firefox.
A theme changes how Firefox looks. A theme could simply change the toolbar's background colors, change how buttons look, or make Firefox look like a completely different program.
There are two kinds of themes, background themes and complete themes. The former changes just your color scheme and background image, while the complete theme changes much more.
Extensions add new features to Firefox or modify existing ones. A popular Firefox extension is AdBlock Plus (installed by default on imaged Lehigh computers), whose purpose ranges from removing online advertising to blocking all known malware domains.
You install an extension in the same way you install a theme, click Add to Firefox button.