fix firefox open export (#786)

components/Editor.js

@@ -97,6 +97,10 @@ class Editor extends React.Component {
       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()
@@ -225,6 +229,9 @@ class Editor extends React.Component {
       if (format !== 'open') {
         link.download = `${prefix}.${format}`
       }
+      if (this.isFirefox) {
+        link.target = '_blank'
+      }
       link.href = url
       document.body.appendChild(link)
       link.click()