The developers of Firefox even long before the release of Firefox 29 "fueled" users new interface Australis. But as always, the new is not always perceived by all users. Some users interface Australis liked, and some are not and they would like to return to the old appearance of the browser that was used for many years.
Sorry for the spelling and phonetic errors in the text.
Owner and main writer of MintGuide.org is not a native English speaker.
You can of course delete the new version and install Firefox 28, but there is another option to stay on the new version of 29, with the return of the old interface, without losing enhanced the functionality of the browser, just by installing custom addition Classic Theme Restorer (Customize Australis).
Click the following link in Firefox: https://addons.mozilla.org/en-US/firefox/addon/classicthemerestorer/