Add display:table-row-group class to manage width of floated form controls

Created by: thgreasi

Hi there. I'm facing an inconsistency issue (between Firefox and Chrome) when using floats on a multi-line "form" that contains input-groups, as demonstrated here.

A workaround that I ended-up was to wrap every input-group with a form-inline, but obviously this doesn't have exactly the same result.

After some hours of searching and since I couldn't find something relevant (sorry if this ends up to be a duplicate), I decided to report this here and get an official suggested way to approach this use case (which would hopefully be useful to others as well).

Tested with Bootstrap v3.3.6 on Firefox 48.0a2 and Chrome 49.