I write some years later and i am older too ... but i found this response trying to pretty print a block of code so i leave tracks of my workarounds.
You can always open js objects in console log clicking on related arrows on the left.
Example:
or you can use as stated before the JSON.stringify() method
If you whant to pretty print a block of js code minimized in a long line add somewhere at the beginnig of code a debugger statement, than paste to the console and run thwe code. The Debugger statement will be reached and the code will be opened into "sources" panel. Here you can use the pretty print button. Pay attention, for your security, to put your debugger statement prior of each other executed statement.
Example:
((function(){/*AutoFill_LastPass*/_LPG=function(i){debugger; return document.getElementById(i);};_LPT=function(i){return document.getElementsByTagName(i);};if(_LPG('_lpiframe')){_LPG('_lpiframe').parentNode.removeChild(_LPG('_lpiframe'));}if(_LPG('_LP_RANDIFRAME')){_LPG('_LP_RANDIFRAME').parentNode.removeChild(_LPG('_LP_RANDIFRAME'));}_LASTPASS_INC=function(u,s){if(u.match(/_LASTPASS_RAND/)){alert('Cancelling_request_may_contain_randkey');return;}s=document.createElement('script');s.setAttribute('type','text/javascript');s.setAttribute('src',u);if(typeof(window.attachEvent)!='undefined'){if(_LPT('body').length){_LPT('body').item(0).appendChild(s);}else{_LPT('head').item(0).appendChild(s);}}else{if(_LPT('head').length){_LPT('head').item(0).appendChild(s);}else{_LPT('body').item(0).appendChild(s);}}};_LASTPASS_INC('https://lastpass.com/bml.php'+String.fromCharCode(63)+'v=0&a=0&r='+Math.random()+'&h=456d3ca99bf926f1727a6944fa06db246df102044140c09f0c9922b6ab1fa88a&u='+escape(document.location.href));_LPM=function(m){var targetFrame=_LPG(m.data.frame);if(null!=targetFrame&&typeof(targetFrame)!='undefined'&&typeof(targetFrame.contentWindow)!='undefined')targetFrame.contentWindow.postMessage(m.data,'*');};if(window.addEventListener){window.addEventListener('message',_LPM,false);}else{window.attachEvent('onmessage',_LPM);}var t=document.createElement('iframe');t.setAttribute('id','_LP_RANDIFRAME');t.setAttribute('sandbox','allow-scripts');t.frameBorder='0';t.setAttribute('src','https://lastpass.com/bml.php?u=1&hash=1&gettoken=0&donotcache=1407688374608280546');t.setAttribute('onload',"document.getElementById('_LP_RANDIFRAME').contentWindow.postMessage('ae24188b13eef4ddac2c37d1c449c47156d0a136c7db1d2ca0bd68060bffcc79','*');");if(typeof(window.attachEvent)!='undefined'){if(_LPT('body').length){_LPT('body').item(0).appendChild(t);}else{document.getElementByTagName('head').item(0).appendChild(t);}}else{if(_LPT('head').length){_LPT('head').item(0).appendChild(t);}else{_LPT('body').item(0).appendChild(t);}}})()); Result of running this code in console: 
