For some reason, Firefox completely discards the ADD_DATE and
LAST_MODIFIED attributes if they are set to 0. This has been
confirmed by exporting a sample set of bookmarks generated by
Nix using home-manager and comparing it to the same sample of
bookmarks set manually and then exported.
Missing these attributes can cause problems for extensions and
other tools that try to read bookmarks. A known example is the
Tridactyl extension.
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