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.
Ma ibenk yeffɣen seg tuqqna d tidet deg-s ccekk, akken ad tḥerzeḍ tilɣa-k•m, ilaq ad tbeddleḍ { -product-firefox-account } awal-ik•im uffir deg yiɣewwaren n umiḍan-ik•im. Ilaq daɣen ad tbeddleḍ kra n wawal uffir i teskelseḍ deg { -brand-firefox } s tira n about:logins into the address bar.