From MozillaZine Knowledge Base



This preference determines whether or not Mozilla applications will periodically retrieve a blocklist from the server specified in extensions.blocklist.url.

While Mozilla’s add-on system is a powerful feature, it can also be a vector for malware. Starting with Firefox 2.0, specific extensions can be blocklisted from a central server (by default, In current versions, the blocklist is not only used for malicious extensions but also to disable vulnerable plugins & crash-prone graphic drivers. The information retrieved from the blocklist is stored in the file blocklist.xml. A current list of blocked add-ons can be viewed here.

Possible values and their effects


Enable the blocklist. Retrieve the list from the server specified in extensions.blocklist.url at the interval specified in extensions.blocklist.interval. If blocklisted extensions or plugins are already installed, disable them, and prevent blocklisted extensions from being installed in the future. (Default)


Do not retrieve a blocklist and do not restrict extension installation.

First checked in

2006-03-08 by Robert Strong

Has an effect in

  • Mozilla Firefox (trunk builds after 2006-03-08; 2.0)

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