Are there any Firefox profiles in the location used by Firefox for profiles in the Windows.old backup?

• C:\Users\<user>\AppData\Roaming\Mozilla\Firefox\Profiles\<profile>\

• https://support.mozilla.org/kb/restore-bookmarks-from-backup-or-move-them
• https://support.mozilla.org/kb/Recovering+important+data+from+an+old+profile

Did you notice any other major changes in settings or missing add-ons? In that case, please check for an Old Firefox Data folder on the desktop and see whether there are any semi-randomly-named folders inside with recently updated files. This would appear if Firefox's Refresh function ran.