What is the computer that has the data? What is the computer that is not getting the data?

On the system with the data; We need to look at the sync logs. Type about:sync-log<enter> in the address bar.

Open the last file created and Copy its contents Now Paste it into this forum.

If the file is too large;

Open a text/word program and load the file. Left-click once. Now <Control> A to highlight everything, then <Control> C to copy it.

Next, have your web browser go to; https://pastebin.com/

Paste <Control> P the content of the file in the window. Note: On the bottom, fill out the boxes as best you can.

Now press Create A New Paste. The page will reload. Copy the new web address, and post it here.

Corrected the above response, The log from the system With the data.

What about another device connected to that Sync account? Is your Firefox data still present on that device?

Thanks FredMc-D and the-edmeister for your response. As this is official PC so only this Desktop is used for this particular account. The log file link is as below:

https://pastebin.com/NBTEasvt

Okay. Now on the unis that is not syncing, do the same thing.

I have only one machine with this firefox account. Actually I have re installed the Windows OS. After that when I installed the Firefox and log in my account it is not reflecting old contents.

Sync isn't intended to be used a backup medium for a solitary device. Mozilla created it to synchronize Firefox data across multiple installations.

For reinstalling the operating system, backing up the entire Profile is advised; then copy the files that are in the backup into the newly created Profile in the fresh Firefox installation.

Per that Sync Error Log, it looks like only Add-ons were enabled on that device. So if that was the user settings in the past, you don't have any bookmarks or Logins data sitting on the Sync server and there is noting to sync back to that device.

1557187097184   Sync.Doctor INFO    Skipping check of passwords - disabled via preferences
1557187097184   Sync.Doctor INFO    Skipping check of bookmarks - disabled via preferences
engines qualify

You could try enabling those setting in Options > General -> Firefox Account - Sync Setting and see if Sync does have that data.

I have done this before and never faced such issue. All options are already have tick sign. i.e bookmarks, open tabs, add ons, history, logins, options. But old data is not recovered.

I have done this before and never faced such issue. All options are already have tick sign. i.e bookmarks, open tabs, add ons, history, logins, options. But old data is not recovered.

Hello there I have been using my Firefox account for a few months and I always signed in to my account after reinstalling my windows and had all my bookmarks and history available. However, today after I reinstalled a windows and signed in to my Firefox account, none of my previous bookmarks and history are available. How can I recover the data? My account is all blank and there is no data there no passwords, bookmarks, or history. Best