If a site stores data in your browser, it can use either:

• Cookies
• Local Storage

Firefox generally saves cookies and site data by default, even during updates, but features, add-ons, or external programs that clear cookies can flush them. Unfortunately, there are no regular backups of the cookies file (cookies.sqlite) or storage databases.

Since your last backup appears to be so old, I wonder whether your Firefox started up in the wrong profile. Could you try this:

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 other profiles that have more recent data?

Okay, re-reading your question, you checked the dates on other profiles already?

The next thing I would suggest is to go data mining in Windows system restore points -- do not use the actual system restore feature, as that can delete more recent data.

Windows often makes backup copies of Firefox profile data when you do system updates, so you can use a tool like one of the following programs:

• ShadowExplorer: http://www.shadowexplorer.com/
• Shadow Copy View: https://www.nirsoft.net/utils/shadow_copy_view.html

Note that you should set Windows to show hidden files and folders before diving in:

https://support.microsoft.com/en-us/windows/show-hidden-files-0320fe58-0117-fd59-6851-9b7f9840fdb2

Then within the most recent restore point shown in the program, you can explore along this path to see whether you can find a shadow copy of your profile:

\Users\your-user-name\AppData\Roaming\Mozilla\Firefox\Profiles\your.profile

If you find a recent cookies.sqlite file, you can export it to your currently live desktop. The storage folders are more complicated, but look for

\storage\default\https+++[yoursite]

You could export that entire folder out to your currently live desktop and we'll try to figure out a way to use it.

Anything interesting in there?