From MozillaZine Knowledge Base
"bookmarks-(date).html", in the bookmarkbackups folder, is a backup of "bookmarks.html" in Firefox versions prior to 3.0. Firefox will automatically generate one of these files the first time it is opened each day. If something happened to "bookmarks.html", "bookmarks-(date).html" could be renamed and used in its place.
This file can be edited in the same manner as "bookmarks.html", but there's no reason to do so.
This file can be moved to a different profile without any extra effort.
Deleting this file will have no ill effects other than losing a day of backups.
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