Navigation:
Turn off Safari's image cache: When you browse the Internet, Safari creates two images of the contents of each webpage viewed (a JPEG and another PNG). These images are used as seen when viewing the Top Sites or History. You can use this option to turn on or turn off the creation of these images.
Turn on single window mode: Some webpages have links opening a new window. You can use this option to open these pages in a new tab.
Search option by default: With OS X Mountain Lion, search by keywords in a webpage is, by default, on the beginning of words (Starts with). You can use this menu to change the default behavior by doing research anywhere in a page (Contains).