Huge FAIL. Apparently uninstalled itself after ONE day. Reinstall does not work properly; it cannot find any matching logins/passwords even though they ARE present in the Key program itself. USELESS until F-Secure fixes their products. Don't depend on this extension.
Update: F-secure corporation has confirmed to me that this extension is problematic and/or no longer working properly for some or all Firefox customers using 82+ and some other branches. I have relayed this info to Mozilla.