Initially it did not work as expected. Turned out I did not understand settings.

I opened an issue and the author answered to make this clear.

"text" is the name of the collection which will appear in the drop down box (which is empty otherwise) and path is the full name of a rdf file, existent or not, empty or not.

So giving the rdf of an old scrapbook (usually something like C:\Users\BUDDY\AppData\Roaming\Mozilla\Firefox\Profiles\lrwtavtr.default\ScrapBook\scrapbook.rdf) plus a name will give you all old data back.

Absolutely great!