Safari for Mac OS X supports extensions that add functionality to the web browser. Extensions can show helpful information about a webpage, display news headlines, help you use your favorite services, change the appearance of webpages, and more. Here’s how to find and install extensions.
The Safari Extensions Gallery lets you conveniently browse extensions and install them with a single click. It's the safest place to download Safari extensions, because all extensions in the Gallery are reviewed, signed, and hosted by Apple. And all extensions that you install from the gallery update automatically.
Open the Gallery by choosing Safari Extensions from the Safari menu. Click “Install now" next to the extension that you want to install.
You can also get extensions directly from your favorite developers. When you download an extension from a developer, you get a file that ends with .safariextz. Double-click the file to install the extension. It isn't signed or hosted by Apple, so Safari asks you to confirm that you trust the source and want to install the extension.
If you want to disable or uninstall an extension, Choose Preferences from the Safari menu, then click Extensions. Select an extension from the list. Turn off the extension by deselecting the Enable checkbox. If you can't determine what an extension does, or you don't expect to use it again, click the Uninstall button.