Did you previously had pages pinned to some of the tiles ? Pinned pages are stored in a pref on the about:config page, so if this file gets reset or you lose this pref otherwise, then you lose the pinned tabs and Firefox will fill them from the history.

Changes made manually on the Firefox Home page are stored in prefs that you can find on the about:config page. You can possibly backup the pinned pref to be able to recover pinned tiles. If you use dismiss a lot, then the blocked pref can grow quite large, an alternative is instead using remove from history.

• browser.newtabpage.pinned => websites pinned to a tile
• browser.newtabpage.blocked => websites removed by clicking Dismiss in a tile
• https://support.mozilla.org/en-US/kb/about-config-editor-firefox

Yes, I had several pinned pages. I have not changed my pinned-page preferences for months, yet now the pinned pages are no longer visible. My prefs.js file lists the pinned pages that I see today--which is an obsolete list--and I have no idea where FF found that old list.

It's pretty clear that FF somehow lost my most recently pinned pages list and replaced it with an old list.

Any ideas on how to recover what I had a couple of days ago? What does it mean, "possibly backup the pinned pref to be able to recover pinned tiles"?

Thanks!

Maybe check this:

• https://support.mozilla.org/en-US/kb/recover-user-data-missing-after-firefox-update

Thanks for this reference. Unfortunately, I've already checked for other profiles, and the only one with any real data in it is the current one. There is one old profile that is essentially empty (only files are parent.lock, times.json, and cookies.sqlite).

I'm guessing that there is no way to recover these. In the future, I probably should include key FF files like prefs.js in my regular backup so I can recover from issues like this.

Meanwhile, I've mostly rebuilt my New Tab Page from memory and with a little searching on the interwebs. I'm missing a couple of pages, but I'm sure I'll run across them sometime and save them again.

Again, thanks for your help, and have a good day.

No "Old Firefox Data" folder on the desktop as well?

Sorry, no such folder.

Did this happen while signed into a sync account?

Yes, and I did sign in on a different computer a few days ago--one that I hadn't used for months. What is the protocol for syncing in situations like that?

You can exclude pinned tabs from Sync via its services.sync.prefs.sync control pref.

• about:config => services.sync.prefs.sync.browser.newtabpage.pinned => false

It doesn't seem so simple.

In addition to the setting you cited, I found this boolean value set to true. It remains in bold no matter which value I set, leading me to believe it is a custom value: services.sync.prefs.sync-seen.browser.newtabpage.pinned I left it as I found it (true).

The one you mentioned was set to true. I changed it to false as you suggested: services.sync.prefs.sync.browser.newtabpage.pinned

This appeared at the bottom of the about:config list immediately after I changed the above to false: services.sync.prefs.sync-seen.services.sync.prefs.sync.browser.newtabpage.pinned = true I left it alone for now.

Can you explain these various settings?

Just in case, I saved the current list of pinned icons.

My next step would be to go back to computer #2 and open FF there. If nothing changes on computer #1, I could revert all the settings there and open FF on computer #2 again and expect it to sync.

I'll wait a while, though, to see if you have any additional thoughts based on these other settings.

Thanks!

On computer #1, I just now changed the following setting back to true: services.sync.prefs.sync.browser.newtabpage.pinned

As it was the only setting I had changed, I went to computer #2 and opened a new tab.

The tab icons shown on both computers remained the same (they did not sync).

It makes me wonder whether my original problem was just a rare glitch.

I don't know how sync is really supposed to work, but it seems to me that it shouldn't replace new things with old things--yet that is what it did a couple of weeks ago with the new-tab icons.

For now, I think I'll let this one rest.

The presence of services.sync.prefs.sync-seen.browser.newtabpage.pinned probably means that Firefox has noticed a browser.newtabpage.pinned pref on one of the other devices connected to Sync with its control pref enabled. I don't know if you need to set services.sync.prefs.sync.browser.newtabpage.pinned to false on all devices to disable syncing browser.newtabpage.pinned on all devices, the same for enabling syncing this pref.

• https://searchfox.org/mozilla-release/search?q=sync-seen&path=

See PREF_SYNC_SEEN_PREFIX:

• https://searchfox.org/mozilla-release/source/services/sync/modules/engines/prefs.sys.mjs