YSK that if you want to view a user's old profile instead of the new looking one, you can make a simple bookmark to quickly switch to it.

Personally I dislike the new profile pages and was looking for an easy solution to view the old style.

If you want to do it manually, just add /overview to the end of the URL. However, you can also make a bookmark for your bookmark toolbar which sits below the URL bar:

javascript:document.location=document.location+"/overview" 

Now when you're on a user's profile with the new format, click that button and you have the old style back.

(I don't think this will work on mobile)