fieldset html element cannot be styled via css

i first notziced this issue in the "find contacts" (/civicrm/contact/search/basic) page:
the form is too broad for my layout, so i wanted to add an overflow:auto to my css.
but that would have no effect.

after some googling the issue i learned, that the fieldset element "is not fully controllable via css" in firefox.
see eg http://www.thescripts.com/forum/thread673236.html
(also i learned, that every fieldset must have a descendant legend element, but that's another issue and no problema descendant for me)

would it be possible as a cure to give every fieldset element an inner div element to fully control its appearance?
flagging this as critical, because it is a real showstopper here, if half the form cannot be made accessible.