Hi waverlytrash, I am sorry, once they have been deleted this cannot be undone.

Windows may have created a backup of your cookies.sqlite database during system updates or backups. I'm not sure it makes sense to look for a potentially week-old file, but if you're curious...

This is trickier on Windows 8 than on Windows 7, and you might benefit from using a third party utility. These were mentioned in another thread:

• http://nicbedford.co.uk/software/systemrestoreexplorer/
• http://www.shadowexplorer.com/

Or... I read about a roundabout way to get Previous Versions on the Properties dialog in Windows 8. I can't test this myself, but here's what you do:

In the address bar of your Windows Explorer dialog, replace the current path with the following and press Enter:

\\localhost\c$

Then click at the end and tack on the following (with your username) and press Enter:

\Users\username\AppData\Roaming\Mozilla\Firefox\Profiles

That should get you in the vicinity of your profile folder. Double-click into that and right-click cookies.sqlite > Properties > Previous Versions to see what might be available. To avoid corruption or crashing, please restore to a different location, exit Firefox, rename the current cookies.sqlite to something like cookies.20150521 and only then copy the old cookies.sqlite into the profile folder.

Note that easiest to prevent such a mistake is to use the Delete key to remove selected cookies and not click the button with the mouse.