add-on locations

I've used my Thunderbird on my usb since forever, but I do keep a backup copy of it on my desktop, which I sometimes access for a quickie.
One thing I noticed a while back is that when I removed adds-ons or themes on my usb, and then transfer my usb copy to my desktop, I see the older add-ons/themes I had removed from my usb, but were still on the older version which I just copied over into the same directory.

My questions is if there is a file or folder that I can delete that has all the add-ons or themes (it could be 2 places) so that when I copy the usb version over the desktop version, it will have the same set of addons/themes.