From FAQ at http://adblockplus.org/en/faq_project#filterset.g

"Do I need to install Filterset.G Updater?

No. Actually, it is recommended not to use Filterset.G with ....... Plus. There are several reasons for this:

* Filterset.G has been intentionally made incompatible with the built-in subscriptions feature in ....... Plus, updating Filterset.G requires a separate extension which basically duplicates existing functionality.
* Filterset.G is not optimized for use with ....... Plus, it will slow down your browsing considerably more than any other filter list.
* Filterset.G makes heavy use of very complicated regular expressions with the consequence that finding the source of problems is difficult and fixing those problems is even more so. In fact, Filterset.G is fixing most problems with exception rules which creates a problem on its own (see next point).
* Filterset.G contains a considerable number of exception rules. This is a big problem because exception rules cannot be overridden. It happened on several occasions that exception rules from Filterset.G whitelisted actual ads making these ads unblockable — something users usually blamed ....... Plus for.

While Filterset.G has had its uses in the past, nowadays other filter lists are certainly a better choice. If you already have Filterset.G Updater installed, you can uninstall the extension and remove the Filterset.G subscription in the ....... Plus Preferences dialog. Feel free to choose any subscription from the list then."