Yes 'Engine', loading of the Sherlock plugin from disk has already been disabled in FF 24. The pertinent section in the first link above also states that further steps to remove support are coming.
It is probably only important to older websites, if any.
I forgot to mention in the original post that:
Firefox Extended Support Release 24 has also been launched.
According to what I have read, it should be identical to the standard FF 24.
But it will not update again until Firefox ESR 31, with only security updates till the standard desktop FF works its way up to 31 over the next year.
Designated for slow moving organizations.
I am not really organized, but I have achieved a very successful workflow and configuration with FF ESR 17 and approx 70 add-ons ;O)