Why did this happen?

The version of this extension, theme, or plugin was deleted by the author(s) and has therefore been restricted by Mozilla.

What does this mean?

When an add-on is deleted, it will no longer be available for download from addons.mozilla.org. If it's already installed, it will be disabled and users will be informed. They may choose to enable the add-on again at their own risk.

Why does Mozilla restrict deleted add-ons?

When the author deletes their add-on, it's no longer maintained or updated, which could compromise Firefox security, stability, or performance. To prevent this, the add-on will be restricted from general use to protect Firefox users. For more information, please read this support article.