Follow-up to Bug 1288591. When using arrow keys to increment/decrement values on each of the field, we should consider step. For example, if type=time and step is 2 minutes. When using up/down keys in minute field, minute should increment/decrement by 2 each time.

The step attribute itself seems not to be supported, also not with the `dom.forms.datetime` and its sub-components enabled in Firefox Nightly. The UI in general should behave like in Chrome, where if you add `step="300"` the seconds are not editable anymore and the only possible steps are 5 minute-steps and hours to enter. Currently, Firefox just displays a HH:MM:SS field and the increment/decrement arrows in the field.

(In reply to info from comment #2) > The step attribute itself seems not to be supported, also not with the > `dom.forms.datetime` and its sub-components enabled in Firefox Nightly. > > The UI in general should behave like in Chrome, where if you add > `step="300"` the seconds are not editable anymore and the only possible > steps are 5 minute-steps and hours to enter. > > Currently, Firefox just displays a HH:MM:SS field and the > increment/decrement arrows in the field. The step attribute is supported. You can try <input type=time value="12:30" step="300">, then if you change the value to "12:32", you get a step mismatch validity state (red border with a error message when you move your mouse over the input box). It's just not reflected when you use up/down arrow keys. (Just a side note, in Chrome, if you change the step to "420", using up/down arrow keys will display all the values) Morpehus, per https://mozilla.invisionapp.com/share/GU7VBIB4D#/screens/171579445 Section D, we're not going to support "increment/decrement values based on step when using arrow keys", right?

The bug was opened at UX spec v1.3, and we did have increment/decrement values change back then. However, considered of resource and consistency, the conclusion was to descoped this feature and I updated the spec to v1.4 on 8/17/2016 accordingly. From my point of view, I still think this feature provides a great value to users, but we are still lack of resource and time, so I would suggest keeping this as a backlog for now.