For reasons incomprehensible to me, Firefox is using non standard
jsonlz4 file format to store bookmark backups.
You can forget about standard console based utilities to extract its contents as I have already tried this without any success.
It is a huge let down.
Install required dependencies.
$ sudo apt-get install build-essential liblz4-dev
Clone git repository.
$ git clone https://github.com/andikleen/lz4json.git
Change working directory.
$ cd lz4json
Compile application from source code.
Pass a compressed bookmark backup file as an argument to application, uncompressed data will be printed to stdout.
lz4json$ ./lz4jsoncat ~/.mozilla/firefox/profile.default/bookmarkbackups/bookmarks-2015-07-30_20.jsonlz4