Where can i find the "Keystore File"

Sorry about my english.
My computer crashed yesterday,then i turn off the computer and go to sleep.now i turn it on,open firefox and click metamask,only show up a white frame whit nothing on it. so i reinstall it ,now it is ok but no account record,i never save seed words and private keys,because i only need this new account for few days,now i am paying for my laziness.
So i come here to ask for help, and i find a thing called “keystore file”, How can i find it ?please help me!