Workaround slides, overview been cutoff and text became blurry in Firefox 47+

Author: jackycute

public/css/slide.css

@@ -243,4 +243,13 @@ pre.mermaid > svg {
     border: none !important;
     box-shadow: none !important;
     margin-bottom: -.25em !important;
+}
+
+.reveal .slides, .reveal .backgrounds, .reveal.overview {
+    transform-style: preserve-3d;
+}
+
+.reveal .slides > section,
+.reveal .slides > section > section {
+    transform-style: flat;
 }