Add-on being blocked by Firefox

Hi, I’m a dev from 360 Internet Protection.

We’ve completed NPAPI removal to support FF52 and the new version,2.1.5, has been listed now.
However, we’ll still getting warning and unable to install new add-on.

Can anyone help?

Note:
The warning is:
360 Internet Protection could not be installed because it has a high risk of causing stability or security problem.

Note: being followed up on this bug report.