McAfee Anti-Spam Thunderbird Extension 2.0 and lower has been blocked for your protection.

Why was it blocked?
These versions of this add-on are known to cause frequent crashes in Thunderbird.
Who is affected?
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.