If you use a recent version of Safari on your Mac to browse the web, you may notice some sites that take forever to load, or don't load entirely, even on a speedy internet connection.
One trick I found that has helped my situation, is disabling Safari's DNS prefetch feature. There isn't a toggle in the preferences for this, but a quick trip to the Terminal can turn it on or off easily.
Make sure to quit out of Safari first. Then go to /Applications/Utilities to locate the Terminal application. Copy and paste the following, then hit Enter/Return.
defaults write com.apple.safari WebKitDNSPrefetchingEnabled -boolean false
In theory, DNS prefetching is supposed to make navigating the web feel snappier, but for whatever reason it seems to often have the opposite effect. Try it out, your mileage may vary. Restoring to the default setting is also straightforward.
defaults delete com.apple.safari WebKitDNSPrefetchingEnabled