Thanks for the code it saved me a headache. I know someone might grumble about resurrecting old thread, but this information needs a correction.

A quick fix for anyone interested i.e. DFIR people. In my case I had to use the following query:

SELECT a.content, b.content, c.content from moz_annos a, moz_annos b, moz_annos c
    where a.place_id = b.place_id and b.place_id = c.place_id
    and a.anno_attribute_id = 12
    and b.anno_attribute_id = 13
    and c.anno_attribute_id = 14;

In case you will get unexpected or no results you can find the correct IDs in the "moz_anno_attributes" table.

You are looking for names:

downloads/destinationFileURI
downloads/destinationFileName
downloads/metaData

and their corresponding IDs.

So in my case the OP's code returned nothing, but after changing the ID's I got my Firefox download list. For easy access I suggest using SQLite Manger addon for Firefox, easy and fast to use, just point to the places.sqlite file and run the query from the "Execute SQL" tab.