How to turn the new Firefox 29 into the old Firefox

” Firefox 29 will introduce changes to the web browser that will rock the world of some users of the browser. The version of Firefox ships with Australis, a design, layout and feature change that introduces major changes to Firefox and is in my opinion comparable to the major switch from Firefox 3 to 4.
“So what are those changes? …”

Source: gHacks Technology News
 How to turn the new Firefox 29 into the old Firefox