HTML and JSON are two different formats. There are separate menu items for importing bookmarks from each format — make sure you pick the right one.

   Import Bookmarks from an HTML file

(https://support.mozilla.org/en-US/kb/import-bookmarks-html-file)

   Restore bookmarks from backup or move them to another computer 

(https://support.mozilla.org/en-US/kb/restore-bookmarks-from-backup-or-move-them)

refer this link https://support.mozilla.org/en-US/questions/960206

It is possible that this copy of places.sqlite is corrupted if your bookmarks aren't restored and in that case you can't use this file and will have to delete all the places files (-shm and -wal as well) If you also have a copy of the JSON backups in the bookmarkbackups folder then try to restore the bookmarks that way.

• http://kb.mozillazine.org/Backing_up_and_restoring_bookmarks_-_Firefox
• https://support.mozilla.org/kb/restore-bookmarks-from-backup-or-move-them

You can check for problems with the places.sqlite database file in the Firefox profile folder.

• http://kb.mozillazine.org/Bookmarks_history_and_toolbar_buttons_not_working_-_Firefox
• https://support.mozilla.org/kb/Bookmarks+not+saved#w_fix-the-bookmarks-file

See also:

• Places Maintenance: https://addons.mozilla.org/firefox/addon/places-maintenance/

These can't get your data back, but will help in the future.

These add-ons can be a great help by backing up and restoring Firefox

FEBE (Firefox Environment Backup Extension) {web link} FEBE allows you to quickly and easily backup your Firefox extensions, history, passwords, and more. In fact, it goes beyond just backing up -- It will actually rebuild your saved files individually into installable .xpi files. It will also make backup of files that you choose.

OPIE {web link} Import/Export extension preferences