how do i chainge the black text in the home screen to white?

i really need this colour switch pls. my firefox kept crashing with no explanation (maybe some extension i had, then deleted when the crashes began) so i had to reset the whole thing. now the appearance has changed. i had put back my background picture, witch was fine with me, but the text was black instead of white like it used to. and it makes me use firefox less. i think its something to do with the website contrast but I'm not sure.