My reasons for giving F&L as a possible maker ;
The black base with aventurine on top is a common feature for F&L, in one of their better known designs (shown on page 54 of Paperweights by Sibylle Jargstorf and paperweight #4 on this page on Alan's site
) the black base with aventurine is used as a background for a scattering of millefiori.
IMHO the technical quality of F&L paperweights are on par with Galliano Ferro and superior to quite a few of the other makers (and quite frankly I think surpasses a lot of the FT designs).
Canes, when used, were usually crisp and clear - not distorted and "squshed" together in the fashion that can be seen in so
many weights made in Murano.
I would be very interested to see similar weights with FT labels as I have not seen FT labeled weights with this base or dome shape before.