Hi, sorry about that, it shouldn't happen of course. So first try restarting Firefox - 3-bar menu > Exit Firefox in bottom right corner. If that doesn't help, please look on your Desktop for a file named Old Firefox Data - [[Refresh Firefox - reset add-ons and settings]]. For bookmarks only, you can try this: Open bookmarks > Show All Bookmarks > Import and Backup > Restore, and see if you have a backup there. If not and for other data, please see - *[[Profiles - Where Firefox stores your bookmarks, passwords and other user data]]. *[[Recovering important data from an old profile]]. ''If your question is resolved by this or another answer, please take a minute to let us know. Thank you!''