Try caching the font

beta/src/styles/fonts.css

@@ -12,7 +12,7 @@
 
 @font-face {
   font-family: 'Optimistic Display';
-  src: url('https://facebookmicrosites.github.io/design/public/fonts/OptimisticDisplayLight-199be98cf48e5b4c688356b08a02362c.woff2')
+  src: url('https://conf.reactjs.org/fonts/Optimistic_Display_W_Lt.woff2')
     format('woff2');
   font-weight: 300;
   font-style: normal;
@@ -21,7 +21,7 @@
 
 @font-face {
   font-family: 'Optimistic Display';
-  src: url('https://facebookmicrosites.github.io/design/public/fonts/OptimisticDisplayRegular-b0e4e99f91efd0021c3ab8e4df0e6e1b.woff2')
+  src: url('https://conf.reactjs.org/fonts/Optimistic_Display_W_Md.woff2')
     format('woff2');
   font-weight: 500;
   font-style: normal;
@@ -30,7 +30,7 @@
 
 @font-face {
   font-family: 'Optimistic Display';
-  src: url('https://facebookmicrosites.github.io/design/public/fonts/OptimisticDisplayBold-3a50548145f36de582c3b36d9626f4d6.woff2')
+  src: url('https://conf.reactjs.org/fonts/Optimistic_Display_W_Bd.woff2')
     format('woff2');
   font-weight: 700;
   font-style: normal;