Font smoothing or anti-aliasing problems

I'm on 10.8.5 (2010 Mac Pro). I am experiencing some problems with font smoothing or anti-aliasing, and would appreciate if someone could tell me what's going on and how to fix it.

Here's how a website used to look in Safari (and still looks like in Firefox):




Here's how the same page looks in Safari Today:



Here's how Safari looks most of the time:



Here's how Safari looks sometimes, but after moving the page it usually goes back to looking like above:



This is how Numbers look when I open it:




This is how Numbers look after I slide the bottom slider a bit to the right: