Hi valentin.mahringer, can you describe anything unusual that happened leading up to this problem? For example: * Added a new device to Firefox Sync * Used Firefox's Refresh function ([[Refresh Firefox - reset add-ons and settings]]) * Uninstalled/reinstalled the same or an earlier version of Firefox * Installed a major Windows update * Something else If you haven't already, please try a regular shutdown and restart of Windows to complete any deferred updates and release file locks. Then check out the following article to see whether any of its suggestions are helpful: [[Recover lost or missing Bookmarks]] Any improvement?