Try adding this to your css code:
.fb-comments, .fb-comments iframe[style], .fb-like-box, .fb-like-box iframe[style] {width: 100% !important;display:block;z-index:2000;position:relative}
.fb-comments span, .fb-comments iframe span[style], .fb-like-box span, .fb-like-box iframe span[style] {width: 100% !important;display:block;z-index:2000;position:relative}
Hope it helps..