Fix Firefox import project bug (#2484)

Firefox is particular about how a form element can submit. It requires the form
to have a button and to be added to the body of the document.

Fixes #1773

readthedocs/projects/static-src/projects/js/import.js

@@ -95,7 +95,8 @@ function Project (instance, view) {
 
         form
             .attr('action', view.urls.projects_import)
-            .attr('method', 'POST');
+            .attr('method', 'POST')
+            .hide();
 
         Object.keys(data).map(function (attr) {
             var field = $('<input>')
@@ -105,13 +106,18 @@ function Project (instance, view) {
             form.append(field);
         });
 
-
-        csrf_field = $('<input>')
+        var csrf_field = $('<input>')
             .attr('type', 'hidden')
             .attr('name', 'csrfmiddlewaretoken')
             .attr('value', view.csrf_token);
         form.append(csrf_field);
 
+        // Add a button and add the form to body to satisfy Firefox
+        var button = $('<input>')
+            .attr('type', 'submit');
+        form.append(button);
+        $('body').append(form);
+
         form.submit();
     };
 }