If you are not intending to upgrade to OS X 10.11 El Capitan for the moment, you should ensure that you download the Safari 9.0 update for OS X 10.9.5 or 10.10.5, as it contains many important security updates, as well as new features.

One major new feature is content-blocking, of course. Security fixes include:

• blocks user interface spoofing on malicious websites, via URL issues;
• a bug which could show LaunchServices’ quarantine history;
• compromised communications between Safari extensions and companion apps, and weak validation of extensions;
• failure to trigger warnings on some malicious websites;
• memory corruption which could have been exploitable;
• an attacker could create unintended cookies;
• leaks of browsing history, network activity, and more to crafted websites;
• cross-origin stylesheets could be loaded incorrectly;
• unauthorised HTTP requests could be sent.

These are important, and merit early updating.

It is available now in the Mac App Store.