There seems to be various JavaScript+browser specific ways of decompressing this, but isn't there some way to transform jsonlz4 files to something unlz4 will read?
How to decompress jsonlz4 files (Firefox bookmark backups) using the command line?
firefox;compression;lz4
I was able to unpack the jsonlz4 by using lz4json:apt-get install liblz4-devgit clone https://github.com/andikleen/lz4json.gitcd lz4jsonmake./lz4jsoncat ~/.mozilla/firefox/*/bookmarkbackups/*.jsonlz4