Download doesn't start with Firefox 33 on master

So I tried the latest master locally with Firefox 33b9. Apparently the download doesn't even start.

Chrome and even IE 10 work fine.

Also, when I try the same link (http://getbootstrap.com/customize/?id=df4c84787ac4f3ff0a5a) on the gh-pages customizer that is published I get

Ruh roh! Could not parse less files.
@gray-darker: lighten(@gray-base, 13.5%);
@gray-dark: lighten(@gray-base, 20%);
@gray: lighten(@gray-base, 33.5%);

I'm not sure if these are 2 separate issues at this point. But locally I don't see any warning at all, not in the console not anywhere else. Are we sure the files on the gh-pages branch are properly updated?