The latest stable version of Firefox (3.6) has certain useful features disabled by default. To enable these features such as Taskbar previews [Windows 7], Tabs previews, etc. you need to manually edit the Firefox’s about :config file.
But the Firefox extension Secrets of Firefox let you do it automatically. Install the add-on from Mozilla Addon site and enable or disable the following hidden features.
- Taskbar previews [Windows 7]
- Tabs previews menu button (far right in the tab bar)
- Open links to the right of the current tab
- Tabs previews (Ctrl + Tab)