The difference between the two security features is that Safe Browsing will compare a visited site to a locally stored list of domains, compared to Enhanced Safe Browser, which will check if a site is malicious in real-time against Google's cloud services.
While it may seem like Enhanced Safe Browsing is the better way to go, there is a slight trade-off in privacy, as Chrome and Gmail will share URLs with Google to check if they are malicious and temporarily associate this information with your signed-in Google account.
Phishing and Malware Protection works by checking the sites that you visit against lists of reported phishing, unwanted software and malware sites. These lists are automatically downloaded and updated every 30 minutes or so when the Phishing and Malware Protection features are enabled.
When you download an application file, Firefox checks the site hosting it against a list of sites known to contain "malware". If the site is found on that list, Firefox blocks the file immediately, otherwise it asks Google’s Safe Browsing service if the software is safe by sending it some of the download’s metadata.