Swap genders on this page (code-golf)
JavaScript, 707 bytes (680 in web console)

javascript:(function(){l=function(s){return s.toLowerCase()};b=document.body;t=b.innerHTML;s="Actress;Actor;Daughters;Sons;Feminine;Masculine;Feminism;Masculism;Feminist;Masculist;Femininity;Masculinity;Mother;Father;Mothers;Fathers;Motherland;Fatherland;Motherhood;Fatherhood;Woman;Man;Female;Male;Females;Males;Girl;Boy;Girls;Boys;Girlfriends;Boyfriends;Grandmothers;Grandfathers;Her;His;She;He;Sister;Brother;Wives;Husbands;WomenWatch;MenWatch;Women;Men;Womensday;Mensday;Internationalwomensday;Internationalmensday;IWD;IMD";a=s.split(';');c=t.split(/\b/);d={};for(i=0;i&lt;a.length;i+=2){x=a[i];y=a[i+1];d[x]=y;d[y]=x;d[l(x)]=l(y);d[l(y)]=l(x)}t='';for(i=0;i&lt;c.length;++i)t+=d[c[i]]||c[i];b.innerHTML=t})()


This is a bookmarklet/favelet; set as URL of a bookmark/favorite and click to transform the loaded webpage.