Suddenly. Firefox won't let me go on the www

Quite suddenly. Right out of the blue. Firefox bars me from going to any websites. Even this forum! I'd already been using the computer for a couple of hours! Will that be because I don't have any anti-virus software on my laptop atm?
I've had to go back onto the Win 10 PC in the mean time!
OK. Panic over! Somehow the date & time setting had got altered and Firefox objected to the wrong month showing. Everything was fine again as soon as it was correctly reset.