gistfile1.js

javascript:(function(){
    var enc=encodeURIComponent,
          w=window,
     frames=w.frames,
          d=document,
         tn=w.getSelection?w.getSelection():(d.getSelection)?d.getSelection():(d.selection?d.selection.createRange().text:0),
         pu=w.location.href,
    isGMail=w.location.host.match(/mail\.google\.com/),
         tt=pt=d.title,
  subjSpans=d.getElementsByClassName("hP"),i,url;

    if(isGMail){
        if(subjSpans){
            tt=subjSpans[0].innerText
        }
        else {
            tt=d.title.substring(d.title.indexOf("-")+1,d.title.lastIndexOf("-")).replace(/^ +/,"").replace(/ +$/,"")
        };
        if(tn!="")tn+="\n\n";
        tn+="From email subject:("+tt+")\n"+pu;
        pu="https://mail.google.com/mail/u/0/?qs=true&search=query&q=subject:("+enc(tt)+")"
    };
    url='omnifocus:///add?note='+enc(tn+"\n"+pu)+'&name='+enc(tt);
    w.location.href=url
})();

// one liner:

javascript:(function(){var enc=encodeURIComponent,w=window,frames=w.frames,d=document,tn=w.getSelection?w.getSelection():(d.getSelection)?d.getSelection():(d.selection?d.selection.createRange().text:0),pu=w.location.href,isGMail=w.location.host.match(/mail\.google\.com/),tt=pt=d.title,subjSpans=d.getElementsByClassName("hP"),i,url;if(isGMail){if(subjSpans){tt=subjSpans[0].innerText}else{tt=d.title.substring(d.title.indexOf("-")+1,d.title.lastIndexOf("-")).replace(/^ +/,"").replace(/ +$/,"")};if(tn!="")tn+="\n\n";tn+="From email subject:("+tt+")\n"+pu;pu="https://mail.google.com/mail/u/0/?qs=true&search=query&q=subject:("+enc(tt)+")"};url='omnifocus:///add?note='+enc(tn+"\n"+pu)+'&name='+enc(tt);w.location.href=url})();