We're sorry to hear about this. If this was a device you really don't trust, you should change your Firefox Account password, and change any passwords saved in Firefox.
Suref-aɣ ɣef aya. Ma d ibenk ur nettwaman ara, yessefk ad tesnifleḍ awal uffir n umiḍan inek Firefox, akked wawalen uffiren imeṛṛa yettwakelsen di Firefox.