Here is just one example I stumbled across in the CSS for a page on WebDirect
background-image:-webkit-linear-gradient(top,#fff 0,#e8e8e8 95%,#cacaca 100%);
background-image:-moz-linear-gradient(top,#fff 0,#e8e8e8 95%,#cacaca 100%);
background-image:-ms-linear-gradient(top,#fff 0,#e8e8e8 95%,#cacaca 100%);
Note the "-moz-linear-gradient", a style specifically for rendering on Firefox browsers. (-webkit handles Safari and Chrome, -ms and the below filter: line handle different versions of IE)
I know Firefox is not supported at the moment, but I can't imagine they would have wasted the effort to add Mozilla specific styles to the themes if support wasn't intended at least at some point in the future.
At first I thought maybe this was just carry-over from v12 when Firefox was supported, but then I remembered that themes weren't even supported in IWP, so that can't be the case.