Type about:sync-log in the URL bar and hit Enter. View the most recent logs and see if you can spot where it failed.

You may post the logs here - http://pastebin.mozilla.org/ - and then provide the resultant hyperlink so a support contributor here can view the log. One sync-log per 'Paste' and under How long should your post be retained? select 'a month'. The Enter key submits the 'Paste' and the URL will change - that is what you need to post here.

the-edmeister said

Type about:sync-log in the URL bar and hit Enter. View the most recent logs and see if you can spot where it failed. You may post the logs here - http://pastebin.mozilla.org/ - and then provide the resultant hyperlink so a support contributor here can view the log. One sync-log per 'Paste' and under How long should your post be retained? select 'a month'. The Enter key submits the 'Paste' and the URL will change - that is what you need to post here.

Thanks a lot for your response. Sorry I re-installed Firefox on all my devices, so it won't be possible anymore to spot where it began to fail :(

I installed the latest version, logged in using my Firefox account and tried to sync several times by clicking the Sync button. Each time I clicked the button Firefox tried to sync, but no sync happened. Each time a new sync error log has been created. I'm posting those logs.

https://pastebin.mozilla.org/8853806 https://pastebin.mozilla.org/8853807 https://pastebin.mozilla.org/8853808 https://pastebin.mozilla.org/8853809 https://pastebin.mozilla.org/8853810 https://pastebin.mozilla.org/8853811

Right now none of my devices have any bookmarks!!!

You're saying that Sync deleted your bookmarks on all your devices?

Any chance that your reset your Sync Password when trying to get Sync to work?

the-edmeister said

You're saying that Sync deleted your bookmarks on all your devices? Any chance that your reset your Sync Password when trying to get Sync to work?

No, Sync didn't deleted the bookmarks. I uninstalled Firefox from all devices, and cleaned all Mozilla folders from my devices. Just in a hope that starting fresh might get me whatever bookmarks I have in Sync Server.

Just found that I still have one laptop that has the bookmarks on it. Not all, not the recent ones, but a lot. But I cannot sync them to my other machines/devices. Because Sync is not working on any machine/device. All of them are running the latest version of Firefox, 42.0.

"I uninstalled Firefox from all devices, and cleaned all Mozilla folders from my devices."

Oh, I think I get it now. That would have disconnected all those devices from the Sync service. Simply "Sign in to Sync" on each of those devices and you should be good.

the-edmeister said

"I uninstalled Firefox from all devices, and cleaned all Mozilla folders from my devices." Oh, I think I get it now. That would have disconnected all those devices from the Sync service. Simply "Sign in to Sync" on each of those devices and you should be good.

"I uninstalled Firefox from all devices, and cleaned all Mozilla folders from my devices" after Sync stopped working (as I said, Just in a hope that starting fresh might get me whatever bookmarks I have in Sync Server).

Right now all my devices are signed in to Sync, and Sync is not working. For test purpose I bookmarked some random pages on each devices (while signed in to Sync) one by one to see if that bookmarks get synced to my other devices. But that didn't happen.

I just posted the sync-error-logs above. And these error logs are being continuously generated each time I click the Sync button or each time Firefox itself tries to sync.

Please ask anything if the situation is still not clear to you.

All of a sudden all my bookmarks are back to all my devices/machines, and Sync is also working fine. :)

Me too, nothing new done by me, but sync just stops. Here is the pastebin url of my log: [paste bin]

That link again (without trying to make it a hyperlink with link icon), since the first time just returns an error when reader tries to open it:

https://pastebin.mozilla.org/8857610