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.

Editing

This file can be edited in the same manner as bookmarks.html, but there's no reason to do so.

Moving

This file should not be moved to other profiles.

Deleting

Deleting this file will not cause any ill effects and may solve some bookmarks issues.

Related files and folders

• bookmarkbackups folder
• bookmarks.bak
• bookmarks.html
• bookmarks-(date).html

Related bug reports

• Bug 157152 - read-only/hidden bookmarks.html (or bookmarks.html.moztmp) causes creation of bookmarks-{n+1}.html