Changing Colour Of Fonts?

[rosyposy]

I changed the colour of the fonts on yahoo mail to blue and now I can't get it back to black, it says it has changed but reverts back to blue when I write anything. I also wanted to change the print to Gabriola regular or segoe print but the same thing happens, and I can't get back to sans serif. Any suggestions please? I have windows 7 and use firefox.