Sorry to hear about this problem. Do you recall Firefox mentioning either of these: (1) It proposed a reset/refresh or tune-up? In the case of a Refresh, a new folder appears on your Windows desktop named Old Firefox Data. Do you see one of those? (2) It said that it needed to create a new profile? This can occur when Firefox thinks you are installing an older version, which isn't a common glitch, but could happen from time to time. Do either of those sound familiar? ---- ''If Firefox did NOT Refresh'' If you haven't already, could you close out of Firefox and do a normal Windows shutdown and restart to complete any pending updates and release any file locks. If Firefox again starts up without your data, could you check whether your stuff is available in a different profile, as follows: '''Profile Manager Page''' Inside Firefox, type or paste '''about:profiles''' in the address bar and press Enter/Return to load it. This page should list at least one profile and could list many. (Each profile has two folders and one or more buttons. Do not use any Remove buttons!) The profile that Firefox is currently using will have this: '''This is the profile in use and it cannot be deleted.''' Do you have any other profile(s) listed on this page? If so, you can check whether it is the one you were using recently by clicking its '''Launch profile in new browser''' button. If it isn't what you want, simply close that new window. If it IS what you want, back on the about:profiles page, click the '''Set as default profile''' button for that profile so Firefox uses it automatically at the next startup. Any progress so far?