makes list-detail template work in firefox Aurora/Nightly

FIxes issue 4 of css-animations ('insertRule doesn't exist in W3C CSSKeyframesRule interface'). See https://github.com/jlongster/css-animations.js/issues/4

The pull request applies the orignal fix of jlongster on the mortar-list-detail repo: 
https://github.com/jlongster/css-animations.js/commit/bedeff09f1e716f8fab5879d385397b0e511ad77