you may be right if you are using Firefox 3.5.x

Your computer's battery for its internal may have died. 01 January 1970 is the beginning of the Unix epoch (link).

Thank you for the warninng. Is there a way to know for sure without going into the PC itself? Some sort of software test?

As my computer is omly 16 months old i was not pleased to think its battery was already dead. a search on google turns up many many people with the same issue and an acknowledgement from mozilla that it is a small bug. i can go back to being amused instead of apprehensive.