Hi greg72, the '''Old Firefox Data''' is created when you use Firefox's Refresh feature. How old are the folder(s)/files in Old Firefox Data? You can turn on the Details view in Windows Explorer to see that at a glance. Normally what happens when you re-run the Firefox installer is that it detects the presence of your previous data and either uses it -- if it's the same version -- or warns you it needs to create a new profile -- if it's an older version. 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 another profile named '''default''' or default-''longnumber'' 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?