Look on your desktop. Do you see a folder called; Old Firefox? Look inside.
Look for the folder with the latest creation date.

https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

https://support.mozilla.org/en-US/kb/how-run-firefox-when-profile-missing-inaccessible

https://support.mozilla.org/en-US/kb/how-run-firefox-when-profile-missing-inaccessible

http://kb.mozillazine.org/Profile_folder_-_Firefox#Navigating_to_the_profile_folder

https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

Type about:profiles<enter> in the address bar.
How many profiles are listed?
How many should be there?
Also, open the profile folder in your file explorer.

Many thanks for taking the time to answer but it doesn't help. There is no folder on my desktop called old firefox, I don't know how many profiles there should be, not even sure what a profile is! I wouldn't know where to begin looking for them. I can get as far as file explorer but have never seen a profile folder - not that I've ever really looked. Thanks anyway. I'll just have to try to recreate it all. Regards Jon Bullock

Hi Jon, a profile is a folder containing Firefox data files. Each profile is like a fresh install of Firefox.

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-release 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?

Hi, thanks to everybody for their help. I eventually managed to find another profile with all my original bookmarks in place. So problem solved. I'm very garetful. Regards Jon Bullock