View/edit a file in a pull request by clicking on the line number.

github.com.js

/**
 * 1) Use http://defunkt.io/dotjs/
 * 2) Install this into ~/.js/github.com.js
 * 3) Click on a line number in the editor to open the file at this position (e.g. to see more context)
 * 4) Alt+Click on a line number in the editor to edit the file at this position
 *
 * This script is based on @agnoster's idea: https://gist.github.com/3906361
 */

function getBranch() {
  return $($('.pull-description .commit-ref')[1]).text().trim()
}

function getURLParameter(sParam) {
  var sPageURL = window.location.search.substring(1);
  var sURLVariables = sPageURL.split('&');
    for (var i = 0; i < sURLVariables.length; i++) {
        var sParameterName = sURLVariables[i].split('=');
        if (sParameterName[0] == sParam) {
            return sParameterName[1];
        }
    }
}

function updateButtons() {
  var branch = getBranch()
  if (!branch) return // couldn't get a branch? NOT A PULL REQUEST

  $('.linkable-line-number').each(function(i, el) {
    el.onclick = function(mouseEvent) {
      var line = $.trim(el.innerText);
      if(parseInt(line)) {
        var baseURL = $(el).first().parentsUntil('.diff-view').last().find('.grouped-button')[0].href;
        var lineParameter = '#L' + line + '-' + line;
        
        if(mouseEvent.altKey) {
          baseURL = baseURL.replace(/blob\/[a-z0-9]+/, 'edit/' + branch);
          lineParameter = '?gotoLine=' + line;
        }

        window.open(baseURL + lineParameter, '_blank');
      }
    }
  })
}

function gotoLine() {
  var line = parseInt(getURLParameter('gotoLine'));
  if(line) {
    $(window).load(function() {
      location.href = 'javascript:editor.ace.gotoLine(' + line + ', 0, false); editor.ace.scrollToRow(' + (line-1) + ');'
    });
  }  
}

$(function() {
  updateButtons();
  gotoLine();
})

Awesome, works great for me!