div 100% tallness works firefox nonetheless ie

i have enclosing div binds twin middle divs; both should take 100% extent 100% tallness within container.

i set both middle divs 100% height. works glorious firefox, however ie divs widen 100% tallness nonetheless wholly tallness calm inside them.

the following simplified chronicle impression sheet.

#container
{
   height: auto;
   width: 100%;
}

#container #maincontentswrapper
{
   float: left;

   height: 100%;
   width: 70%;
   margin: 0;
   padding: 0;
}


#container #sidebarwrapper
{      
   float: right;

   height: 100%;
   width: 29.7%;
   margin: 0;
   padding: 0;
}

is there something i am doing wrong? any firefox/ie quirks i am blank out?