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

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?

Once a block is implemented, Firefox will block the unsafe add-on from loading. Blocks can be issued at varying levels depending on the severity of issues found.

  • Soft blocks disable an extension by default, but allow you to override and continue to use the add-on. Soft blocks are issued for non-malicious add-ons.
  • Hard blocks disable an add-on and do not allow you to enable it or override the block. Hard blocks are used when add-ons are found to be malicious.
  • Click-to-activate blocks disable a plugin by default, but allow you to enable the plugin for particular sites. This type of block is issued for non-malicious plugins.

How will I know if an add-on is blocked?

You will see a notification from Firefox 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.

If the add-on has been hard blocked, you will not be able to override the block.

Can I install an add-on after it has been blocked?

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.

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.

Adobe Flash plugin

End of Flash support: Like other browsers and Adobe, Firefox ended Flash support at the end of 2020. Please see End of support for Adobe Flash for more information.

Firefox can prevent the Adobe Flash plugin from running automatically (which prevents many issues). When Firefox blocks the 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?

Firefox does not allow the Adobe Flash plugin to run automatically, which prevents many issues. If a website uses it, you'll see a prompt to run the Adobe Flash plugin. You can then choose to run the plugin.


To learn more, see Why do I have to click to activate plugins?

What to do if you see a blocklist notification

If the installed add-on is disabled

Accept the notification and restart Firefox. If you choose to override a soft block, you do so at your own risk.

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 (extension or theme):
  1. Click the menu button Fx57menu, click Fx57Addons-icon Add-onsFx57Addons-icon Add-ons and Themes and select Extensions.
  2. Click on the settings icon Add-on Tools Icon 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.

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