Java Plugin 8 update 170 and lower (click-to-play), Mac OS X has been blocked for your protection.

Why was it blocked?
Old versions of the Java plugin are potentially insecure and unstable. All users are strongly recommended to update on java.com.
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.