Make a bookmarklet with this code:

  javascript:(function(){try{var%20url=encodeURIComponent(location.href);var%20ifr=document.createElement('iframe');ifr.style.position='absolute';ifr.style.top=10+'px';ifr.style.left=10+'px';ifr.style.width=450+'px';ifr.style.height=100+'px';ifr.style.border='none';ifr.src='http://www.facebook.com/plugins/like.php?href='+url+'&show_faces=true&width=450&action=like&colorscheme=light';ifr.scrolling='no';ifr.frameborder=0;document.getElementsByTagName('body')[0].appendChild(ifr);}catch(e){}})();

Then you can visit any webpage and "like" it.