[_ck_]

I have another idea why it might only work in firefox.

It’s possible you are somehow sending malformed HTML with a damaged or buggy template and only Firefox is able to interpret it correctly while the other browsers munge the bad code and therefore leave out the missing hidden input fields.

Look carefully at your post-form.php template and see if there is any incorrect HTML. Also try doing a direct download of that ?new=1 page instead of looking at it in a browser and study the source for malformed HTML, for example an <input field without the closing > .

(you could even temporarily replace post-form.php template from the original kakumei theme just to see if it works)