style: improve again font rendering on Firefox

Author: JulienMassonnat

src/scss/main.scss

@@ -11,7 +11,10 @@ html {
 
   h1 {
     font-family: var(--ifm-h1-font-family);
-    font-weight: 400;
+    -moz-osx-font-smoothing: grayscale;
+    -webkit-font-smoothing: antialiased;
+    font-smooth: antialiased;
+    font-weight: lighter;
   }
 
   .footer__title {