See:

• https://support.mozilla.org/kb/Restore+the+default+Smart+Bookmarks+Folders

Reset browser.places.smartBookmarksVersion via the right-click context menu to the default value

• about:config : browser.places.smartBookmarksVersion -> right-click -> Reset

You can open the about:config page via the location/address bar. You can accept the warning and click "I'll be careful" to continue.

• http://kb.mozillazine.org/about:config

I tried to do this exactly including the setting the value to zero or right clicking it and then reset and it doesn't restore my "most visited". When I close and restart Firefox the value is always set to 8.

You must not changed its value, but reset to the value and close and restart Firefox. That would normally bring back the default smart bookmark folders on the next start.

Did you check that they aren't in another folder like Bookmarks Menu?

You can check for problems with the places.sqlite database (bookmarks and history) in the Firefox profile folder.

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

See also:

• 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