Automatically created compressed .jsonlz4 backups in the bookmarkbackups folder include a hash part.

• bookmarks-YYYY-MM-DD_<item count>_<hash>.jsonlz4.

This hash is used to check if there have been changes to the bookmarks and a new backup is only created when the calculated hash value differs from the hash in the most recent backup. This is to prevent older backup from getting overwritten. So it is quite possible that you haven't created new bookmarks or edited existing bookmarks during those gaps. Otherwise there might have been problems with the places.sqlite or other profile issues that have prevented Firefox from creating a backup.

Thanks cor-el. That was my first thought, and it does explain some of the gaps I see. But.. not on a couple of machines where I am very active and there should be very few - if any - days skipped. I use them for different purposes and constantly bookmark sites. What puzzles me is this: I use Sync. Across ALL my PCs. Shouldn't that cause them to all to end up with the same backups? (I'm trying to get a bit more of an understanding about Sync here - as I think it is tied in with this issue)

Thanks very much for your answer anyway. It does help. I'll keep this thread single "core topic" to stay on point - but will probably post another question later today about how Sync works.

Cheers

If you use Sync then best is to disconnect Sync temporarily during troubleshooting.

You can check for problems with the places.sqlite and favicons.sqlite files in the Firefox profile folder.

• use "Verify Integrity" button on the "Help -> Troubleshooting Information" (about:support) page

In case errors are reported with "Verify Integrity" close and restart Firefox and retry.

If "Verify Integrity" cannot repair places.sqlite, rename/remove all places.sqlite and favicons.sqlite files in the Firefox profile folder. Firefox will rebuild places.sqlite and restore the bookmarks from a recent JSON backup in the bookmarkbackups folder.

• keep a backup copy of places.sqlite in case a new places.sqlite database has to be created

See also:

• https://support.mozilla.org/en-US/kb/Bookmarks+not+saved#w_fix-the-bookmarks-file
• https://support.mozilla.org/en-US/kb/fix-bookmarks-and-history-will-not-be-functional

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Directory/Folder:
  Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/Profiles

Thanks cor-el, that's good detail. I'm fine for now so I'll end here. You've given me some knowledge about the structure and the way it hangs together that will help if it plays up - and for me to do a bit of semi-informed exploration. many thanks!