Fix activestorage direct upload on firefox

Direct upload on firefox is not working because it can’t handle click
events on “input[type=submit]”.
After a successful upload we can see on console a xml parse error, it
happens because AWS S3 success body response is empty, so changing the
reponseType suppress this error.

activestorage/app/javascript/activestorage/blob_upload.js

@@ -7,6 +7,7 @@ export class BlobUpload {
 
     this.xhr = new XMLHttpRequest
     this.xhr.open("PUT", url, true)
+    this.xhr.responseType = "text"
     for (const key in headers) {
       this.xhr.setRequestHeader(key, headers[key])
     }

activestorage/app/javascript/activestorage/ujs.js

@@ -53,6 +53,7 @@ function submitForm(form) {
   if (button) {
     const { disabled } = button
     button.disabled = false
+    button.focus()
     button.click()
     button.disabled = disabled
   } else {