from a duplicate thread that was just locked

all bookmarks are gone,i remember my bookmarks were synced..

Is every bit of your data gone from Firefox - like Passwords and browsing history? Or just your bookmarks?

When you open Options > Sync do you see Create an Account and Sign In? If so, try to Sign In.

If you see the Disconnect button in Options > Sync, try using the Sync button in the Customize - Additional Tools and Features after moving it to a toolbar temporarily. https://support.mozilla.org/en-US/kb/customize-firefox-controls-buttons-and-toolbars

yes all the data is gone

i tried all the options you mentioned but no result

after this email,i lost all bookmarks.need help to recover

thanks for your support,i'll add all my bookmarks manually..f*ck firefox

So that email was sent before you posted here? It looks like your Sync account was overwritten with what Sync thought was another device when you first opened Firefox after that upgrade, and that's why your Firefox data disappeared.

Do you have another device running on that same Sync account? If so, don't open Firefox on that device until that device is disconnected from the internet to keep this issue from cascading and wiping your Firefox data from that device, too. Then open Firefox and use the Disconnect button in Options > Sync. From there my advice is to create a new Sync account in that other device and let your data Sync to the server for a good number of hours. Then connect the upgraded Win10 device to that new Sync account to get your data back.

And if that was the only device you had connected to that Sync account, you were using Sync improperly - it wasn't meant to be used on one device as an ersatz backup media. When Windows 10 was installed, did it create a Windows.old folder? If so, you can probably recover your entire Firefox profile from there - in the /Users/username/AppData/Local/Mozilla/Firefox/Profiles/ path.

BTW, after receiving 2 PM's from you while I was composing a response and having a bit of lunch, I will be walking away from my computer for awhile. If my response helped you - fine, you're welcome. If not, someone else will need to help you - my patience disappeared with your impatience.

You can check if you have an C:\Windows.old folder with your old Firefox profile folder.

• C:\Users\<user>\AppData\Roaming\Mozilla\Firefox\Profiles\<profile>\

See:

• https://support.mozilla.org/kb/Recovering+important+data+from+an+old+profile
• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox