The information that you are looking for is not accessible through the Firefox Accounts system.

If you have a concern about device connected to your account, you can remove it. See Manage the devices linked to your Mozilla account for more information.

It's also recommended to change the passwords for your Firefox Account along with accounts that you have on other services.

Hope this helps.

Note that you should disconnect (remove) other devices before changing the password of the Firefox Account.

If a mobile connection was used then the IP wouldn't help much as that would depend on what hotspot was used to connect to internet.

See also:

• https://support.mozilla.org/en-US/kb/ive-lost-my-firefox-sync-account-information