When starting V3 it never asks me if I trust Addon Manager. That seems to be where something is happeing in restricting this from showing up on the drop down list.
P3D never ask to trust anything, this happens only on FSX, so it's normal you won't be asked.
Of course, since you are not being asked for trust anymore, it now becomes more difficult to be sure if you are not being asked because there's a problem, or because you already authorized that module, or because you already trusted us (as a publisher) entirely in your system, or because you *UN*-trusted us entirely on your system, so nothing signed by us will start.
To verify this, you can go to the Control Panel, under "Internet Options", look for the "Content" tab, there should be an "Publishers" button, that will list the software authors that you trusted, and another tab with untrusted authors. If you see "Virtuali s.a.s", remove it from both tabs (especially if it's under untrusted).
If this is not the problem, other reason for the Addon Manager might be checked in this thread:
http://www.fsdreamteam.com/forum/index.php/topic,7545.msg62899.html#msg62899
