I just used Firefox (37.0.2 on Windows) to reply to this post, and it worked fine:
I then tried to reply to this post using Firefox, and clicking on the "Reply" buttons did nothing. No action, no progress, nothing:
I then tried using Internet Explorer (Version 11.0.9600 "Update Versions" 11.0 17) and it worked fine.
What's different between those two pages that stopped this from working?