Browser detection script

{
  "name": "browser",
  "description": "Browser detection script",
  "keywords": [
    "browser",
    "detect",
    "detection",
    "firefox",
    "opera",
    "safari",
    "chrome",
    "ie"  
  ]
}

index.js

// 93 byte length
function(a){a={}.toString.call()[8];return{f:a=='U',o:a=='W',s:a=='D',c:a=='g',i:!a||a=='O'}}
/* alternative 77 byte length
function(){return{U:'f',W:'o',D:'s',g:'c',O:'i'}[{}.toString.call()[8]]||'i'}
*/

test.html

<pre id="br"></pre>
<script>
var b = function(a){a={}.toString.call()[8];return{f:a=='U',o:a=='W',s:a=='D',c:a=='g',i:!a||a=='O'}}();
document.getElementById('br').innerHTML = b.f && 'Firefox' || 
                                          b.o && 'Opera'   || 
                                          b.s && 'Safari'  || 
                                          b.c && 'Chrome'  || 
                                          b.i && 'Ie'      || 
                                                 '???'     ;
</script>

<!-- Alt version -->
<pre id="br2"></pre>
<script>
var b = function(){return{U:'f',W:'o',D:'s',g:'c',O:'i'}[{}.toString.call()[8]]||'i'}();
document.getElementById('br2').innerHTML = {f:'Firefox',o:'Opera',s:'Safari',c:'Chrome',i:'IE'}[b];
</script>