@ Omid:
Extensions are disabled until the final API changes arrive.
Please use the dev channel for the latest extension API.
now strangely, the dev channel is still 4.0.223.11
...and will probably be updated to something above 4.0.223.16 a bit later...if you stick to it, you won't get 4.0.223.16 with extensions disabled. But if you stick to beta, you'll be unfortunately automatically updated to 4.0.223.16