Add-ons that cause stability or security issues are put on a blocklist

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  • Revision id: 163680
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  • Creator: AliceWyman
  • Comment: edits to revision by Caitlin
  • Reviewed: Yes
  • Reviewed:
  • Reviewed by: AliceWyman
  • Is approved? Yes
  • Is current revision? No
  • Ready for localization: Yes
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  • Readied for localization by: AliceWyman
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Starting in Firefox version 57, only extensions built using WebExtensions APIs will work. Not sure if your add-ons are affected? See Firefox add-on technology is modernizing and these Frequently Asked Questions for details.

Blocklisting (or blocking) is an action of last resort taken to protect Firefox users against add-ons (extensions, themes and plugins) that violate Mozilla's add-on guidelines.

What does the blocklist do?

Disables unsafe add-ons

Firefox will block the unsafe add-on from loading and present you with the following message:

Firefox has determined that the following add-ons are known to cause stability or security problems

Add-ons Blocklist Mac1

To prevent these add-ons from running, click Restart Firefox.

Blocks unsafe add-ons from being installed

Once an add-on has been blocklisted, it will not appear in the gallery of until the developer uploads a new version that addresses all issues that resulted in the block request.

Additionally, Firefox will prevent you from installing an unsafe add-on that is on the blocklist by displaying this message:

The add-on name could not be installed because it has a high risk of causing stability or security problems.

Prevents plugins from running automatically

Firefox can prevent a plugin from running automatically (which prevents many issues). When Firefox blocks a plugin you'll see a message similar to this:

Click to play 1 new

You can then choose to run the plugin or update it (if an update is available). To learn more, see Why do I have to click to activate plugins?

Support ended for all NPAPI plugins, except for Adobe Flash, in Firefox version 52. See this compatibility document and this article for details.

What to do if you see a blocklist notification

If the installed add-on is disabled

Accept the notification and restart Firefox.

Extensions and themes

  1. Click the menu button Fx57menu , click Fx57Addons-icon Add-ons and select Extensions.
  2. On the "Tools for all add-ons" Add-on Tools Icon menu, make sure that the Update Add-ons Automatically menu item is checked.


Check to see if there's an updated version of your plugin. If there are no plugin updates available, you may need to contact the developer of the plugin that was blocked.


If you were blocked from installing an add-on, check to see if there is an updated version of the add-on you were trying to install. Please be aware that some blocks may be permanent and you may need to find an alternative add-on.

Can blocks be lifted?

Depending on the severity of the violation, the history of the developer, and other relevant factors, some blocks may be lifted once the developer uploads a new approved version. If that happens, users who had previously downloaded the add-on will immediately be able to use it again once its listing goes live again on

To make sure you are always using the most up-to-date version of an add-on, go to the "Tools for all add-ons" Add-on Tools Icon menu and make sure that the Update Add-ons Automatically menu item is checked.

What unsafe add-ons are on the blocklist?

See the list of blocked add-ons.