If the disconnected device is indeed suspicious, to keep your information safe, you should change your { -product-firefox-account } password in your account settings. You should also change any other passwords you saved in { -brand-firefox } by typing about:logins into the address bar.
We q'eleb'el ri okisab'äl, richin chi jikïl ri awetamab'al, k'o chi najäl ri ewan atzij pa { -product-firefox-account } pa runuk'ulem rub'i' ataqoya'l. Chuqa' k'o chi najäl jun chik xab'achike ewan tzij xayäk pa { -brand-firefox } rik'in natz'ib'aj about:logins pa rukajtz'ik ochochib'äl.