Page hangs after clicking the "sign now" button

Hello,

I’ve received reports that some users had the page hanging after clicking the “sign now” button. I’m running the latest version of the plugin and WordPress version 3.8

https://www.tibetnc.org/get-involved/stand-with-a-fellow-nobel-laureate/

I tried to reproduce this bug by signing from different browsers (Firefox, Chrome, Explorer, etc.) and from different platforms (Mac, PC, iPhone, Android), but on my side everything went fine.

Only one friend was able to reproduce this on his Mac OS 10.6.8 using Firefox 32.

Any help would be greatly appreciated.

Thank you in advance.

https://www.ads-software.com/plugins/speakup-email-petitions/