A solution to Firefox frame rate woes.

Hey guys, just a heads up to others out there who may run into this. We have buttons and other UI elements that are rendered with html dom and css overlayed on top of the webgl canvas. We noticed that the Cesium frame rate in Firefox drops from ~50fps to ~12fps when these are rendered visible. It took a while to find out what was happening, but it seems Firefox does not handle dom elements with any sort of transparency overlaying the webgl canvas. When we made all canvas overllapping dom elements completely opaque and took box-shadow off, the frame rate goes back to an acceptable and usable value. The canvas frame rate also significantly drops in half when the Firefox debugger is active. Chrome handles all of these like a champ.