Resume : All info (password, historic, favorites, everything) stored on a new sync account was lost. Before the problem : I made the new account, syncronized it with my current cookies, once saved i formated the pc. THen logged and did a syncronization on the new distro's firefox, and everything (cookies) was loaded perfectly. That was months ago. The account remained logged this whole time. ( account maded on ubuntu 16.04 or 18.04, and logged on lubuntu 19.04) Problem : Now i re-made this whole process (formating the pc and loggin on this same sync) , but this time there was no data at all. Was like a new account. Maybe even worse, because a new account should have at least one historic page. But this account's historic was totally erased. Even if the account was not syncronizing and saving my cookies after i've logged on the new distro, it did saved the cookies from the old distro, so at least these cookies should be there. (account loaded on lubuntu 19.10) After the problem : After the loss of its data, the blank sync account have beeing sucefully sycronizing (loading and saving) new cookies, but never the old ones. What i tried : Re-syncronized. Re-logged on other devices (android and linux). re-installed firefox. Redifined the password. Why its unlikly i made a mistake : I'm a old user of firefox sync (in other accounts) on a live-linux distro, so i'm constantly loggin into my other Sync account and syncronizing my data. And never i had a problem were i losed my saved historic/favorites/passwords. Anything. So is very unlikely that i made a mistake ... I even have old confirmation emails, proving the account was created on a device, and then logged on a new device, wich required a confirmation password. My conclusion : A sync Account was created, cookies were saved into it, then they were deleted and the browser stopped saving new cookies on the account. I didn't realized because the cookies were alredy stored on my local drive. When i made a new logging, the browser started to save cookies again, and those weren't remains, because they weren't deleted. Could it be that firefox's servers had a malfunction and my data were lost ? Nothing else make sense to me now. Thanks for your help.