The GNOME Project has integrated Gnome icons into Firefox.
Included in the package are some of the most essential Firefox extensions that users might need. These include Adblock Plus, Noscript, Update Notifier, and Tab Mix Plus. Additionally, Gnome Classic supports Addons install buttons that have been removed from latest trunk versions. It's worth noting that this feature can come in handy when you're trying to install some of the more complex add-ons.
One of the best things about Gnome Classic is that it offers great support for most extensions. This aspect alone sets it apart from other Firefox themes that do not have such capabilities. So if you're looking for a vintage Firefox theme and you need support for your favorite extensions, then Gnome Classic is definitely worth checking out.
Version 3.5.0.3: N/A