fix: a11y message behaving strange with firefox due to backdrop-filter

Author: NiclasNorin

assets/source/3.0/sass/a11y.scss

@@ -10,6 +10,5 @@ body.user-can-upload_files {
     font-size: .8em;
     border-radius: 3px;
     border: 1px solid #fff;
-    backdrop-filter: blur(4px);
   }
 }