YouTube Plus Plus 99.7 has been blocked for your protection.

Why was it blocked?
Version 99.7 of the YouTube Plus Plus extension isn't developed by the original developer, and is likely malicious in nature. It violates the Add-on Guidelines for reusing an already existent ID.
Who is affected?
All Firefox users who have this version of the add-on installed.
What does this mean?

The problematic add-on or plugin will be automatically disabled and no longer usable.

When Mozilla becomes aware of add-ons, plugins, or other third-party software that seriously compromises Firefox security, stability, or performance and meets certain criteria, the software may be blocked from general use. For more information, please read this support article.