Post/Page Previews not working

Hey,

Can anybody familiar with the visual editor tell me how does it use the query strong to work?

I’m using this code to block /? from coming in, but it seems to be preventing page/post previews from showing as well:

<IfModule mod_rewrite.c>
RewriteCond %{QUERY_STRING} ^[\-/A-Z0-9]+$ [NC]
RewriteRule (.*) - [R=404]
</IfModule>

I found this code off stackoverflow. I need help to adjust that code to allow previews to show up instead of going to a 404?

Thanks!