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.
Je nam žel to słyšeć. Jeli to bě grat, kotremuž woprawdźe njedowěrjeće, wy měł hesło swojeho konta Firefox a hesła, kotrež su w Firefox składowane, změnić.