It did occur to me that I had a few backup .json files in which Firefox bookmarks were stored. As I did not want to overwrite the existing bookmarks, but I wanted to retreive just a few links, I tried to open the file with a text editor.
The result was not pleasant:
I decided to use some CLI magic to transform this in a list of URLs which is easily readable, instead. It can be done in one line:
$ sed "s/\"uri\"\:\"/\\`echo -e '\n\r'`/g" bookmarks.json | sed "s/\"[^@]*$//" > new_bookmarks.txt
Where: bookmarks.json -> bookmark file name
new_bookmarks.txt -> new file name where the links will be saved