simplify isSafari isFirefox

components/Editor.js

@@ -78,15 +78,15 @@ class Editor extends React.Component {
 
     this.setState(newState)
 
+    if (window.navigator) {
       this.isSafari =
-      window.navigator &&
         window.navigator.userAgent.indexOf('Safari') !== -1 &&
         window.navigator.userAgent.indexOf('Chrome') === -1
       this.isFirefox =
-      window.navigator &&
         window.navigator.userAgent.indexOf('Firefox') !== -1 &&
         window.navigator.userAgent.indexOf('Chrome') === -1
     }
+  }
 
   carbonNode = React.createRef()