Yesterday I logged out of my friend's account on their device '''without selecting the "delete all data" '''by my mistake, and logged into my own which syncs all my bookmarks across accounts. After logging in for about 4 hours, I signed out, read long enough '''to select the "delete all data" checkmark''', and shutdown their computer. This evening, I have realized my account has hundreds of bookmarks unrelated to my account. After some confirmation I now know this information is from the laptop I synced from, and all this data was synced in some 5 hours. Is there a way I can backup my sync data to the morning before this happened? And if I deleted my friends data, can they recover their bookmarks/browser info another way? (they wouldn't have synced to my data since I deleted only mine after I logged out). Sincerely, a panicked firefox user.