.fb-comments, .fb-comments iframe[style] {width: 100% !important;}

<div class="fb-like" data-href="my.domain.com" data-layout="standard" data-send="false" data-width="255" data-show-faces="false" data-action="recommend" data-font="verdana"></div>

$(window).resize(function() {
  var computed_width = $('div.main-content').width();
  $('div.fb-like iframe').attr('style', 'border: medium none; overflow: hidden; height:  24px; width: ' + computed_width + 'px');
});

#fbcomments, .fb_iframe_widget, .fb_iframe_widget[style], .fb_iframe_widget iframe[style], #fbcomments iframe[style] {width: 100% !important;}

#fbSEOComments, #fbSEOComments iframe[style] {width: 100% !important;}