Then you need to contact True key by McAfee support why it doing something that Firefox browser doesn't permit it to do.

Thanks. I have reported the issue to McAfee and they are working on it.

The True Key extension from McAfee cannot be installed on Firefox. When I try to install the True Key extension, a message pops up advising me that the extension cannot be installed due to a Firefox policy violation. I have reported the issue to McAfee for their action. Photo of the pop up message is attached.

Due to violation of Mozilla's policies for Extensions https://extensionworkshop.com/documentation/publish/add-on-policies/

Seems to be a recent thing as there are at least three threads about this today now according to search.

Not the first time a McAfee extension has been added to blocked list as four of their extensions were added to this old blocklist https://blocked.cdn.mozilla.net/ over the years.