From MozillaZine Knowledge Base
bookmarks.html.moztmp is a temporary file used when writing bookmarks. The presence of this file indicates that writing to the bookmarks file has failed and can also cause the creation of multiple bookmarks-(number).html files.
This file can be edited in the same manner as bookmarks.html, but there's no reason to do so.
This file should not be moved to other profiles.
Deleting this file will not cause any ill effects and may solve some bookmarks issues.
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