Editing footer in Twenty Thirteen Theme?

I recently updated the Twenty Thirteen theme on a self-hosted WordPress installation to v3.7, and in doing so accidentally lost changes I had made to the footer. I think I had previously implemented these changes by editing the footer.php file (under wp-content/themes/twentythirteen), but when I tried to mimic these edits in the footer.php now, the changes aren’t showing up on the website. Am I doing something wrong? Did WordPress change how the footer works in the current version of the theme? Any help is greatly appreciated – thanks!