Where this validating message come from?

Question

I wrote a simple form, including text field, textarea, select and some validating by WP_error. When I try to submit the form without filling text field or textarea, I got a popup tip pointing the blank text field, it says "please fill in the field". This is different from the error message I wrote, and I didn't write any ajax for validating-- my validating messages comes after the form submitted and redirected. Is this validating part of WP3.3 new feature? or it's a firefox feature?

Edit: Thanks to joseph, found the reason-- it's html5 new feature-- required attribute

The required attribute applies to all form controls except controls with the type hidden, image inputs, buttons (submit, move-up, etc), and select and output elements. For disabled or readonly controls, the attribute has no effect.

Answer 1

Could you please show us your code or better yet provide an example? Sight unseen, my preliminary thought based on your description is that you are using some of the new HTML5 form elements and/or attributes. In particular, the required attribute would cause the error that you are seeing depending on the browser that you are viewing the page in (Firefox in this case).