Bill D, when you say

Companies, of course, are delighted when their product..(Kleenex, Jello in the US) become synonymous with a class.

I think not so across the board. That's a terrible danger, because the company is likely to lose the identity of its product.

How about Nylon, which became "nylon"
and Eversharp (pencils), which became "eversharp" pencils
and Cellophane, which became "cellophane"
and Aspirin, which became "aspirin"
and Scotch Tape, which became "scotch tape"
I'm not sure whether Celluloid was a trademark which faded into "celluloid", but I strongly suspect so.


and on and on, trademarks which were lost because they became
generic.

Dave Oesterreich