Needs to use the same incomplete & save folders. Not sure how the new version LW works with its incomplete preferences. Traditionally before LW 4.18, inside the incomplete folder were two files called Downloads.dat & Downloads.bak which held the incomplete file history. So selecting the same download folder 'should' at least in previous versions work fine. Now I'm not sure.

Oh .. without the LW download history preference files, the incomplete files will be ignored.

Some people actually use the same download folders & where FW leaves off, LW picks up from when it's opened & vice versa. I think I did this too from memory a couple years ago. I haven't used FW much since then & think I changed the download location eventually, can't remember on my old computer.