An alpha release of Firefox 2.0 is due out in the next few days, according to meeting minutes posted at Mozilla Foundation.
A new feature in the alpha release will be a “blocklist” for certain extensions that are known to contain vulnerabilities that make them exploitable. When someone installs an extension, or updates an extension, then that extension will be checked in realtime over the Internet against the list of blocked extensions. If the extension is in the blocklist then Firefox will alert the user and prevent that extension from being installed. The blocklist will be maintained by Mozilla as a check and balance, and considerable efforts will be made to remove exploitable extensions from popular extension sites.