I don't think that it is possible to convert places.sqlite back to the old scheme used in Firefox 45 as there are a lot of changes to tables like for favicons that are stored in favicons.sqlite and no longer in places.sqlite. If you do not have a backup copy then you will have to remove the new places.sqlite and let Firefox 45 create a new places.sqlite. You should be able to get your bookmarks back, but you will lose the history.

Thank you for your answer. Yes I have backuped file places.sqlite, but he doesn't have some actual information (а some week old file). It's a pity that FF auto convert some user profile files without warnings or save his .old version. It's my understanding, now i have only one way - manual edit .sqlite file in sqlite editor for add missing information from converted places.sqlite... May be FF has built-in functional that export history ( as a bookmarks) in other format and then import it to the .sqlite?

You can look at this utility.

• https://www.nirsoft.net/utils/browsing_history_view.html