The Page Plugin is sort-of responsive and controlled completely by Facebook. Please see their documentation, below:
developers.facebook.com/docs/plugins/page-plugin
Basically, the plugin will resize itself to the div that it's in on page load. If you resize after the page is loaded, it will not resize again. However, if you reload the page, it will resize again. So, in a tablet, it should load properly.. in a desktop browser, after you resize, you need to reload the page to test.
I hope that helps explain,
Alex