The grey color made them a bit more readable, but it looks like either fonts are broken (the text is horizontally doubling!) or it's some font shadow CSS property poorly chosen.

The fact that you don't see the problem immediately makes me also guess if it's just rendering that way only on mobiles or in my browser*os (Cromite on Android) or maybe a result of some resource (js/CSS/woff) getting blocked by the built in adblocker or something.