Safari 12 adds the option for favicons in tabs, as shown above. It’s a small thing but it really does make it easier to see which tab is which at a glance.
If you’d rather not wait until this fall you can download the Safari Technology Preview right now, assuming you’re using macOS High Sierra. These technology previews are occasionally buggy but give you access to new Safari features early. The Technology Preview is installed as a seperate program, meaning you can always fall back on the stable version if things get buggy.
Back to the Favicons. You can enable them in the Technology Preview by heading to Preferences > Tabs and checking the “Show website icons in tabs” option, as shown above.
It will showed up like this on your Safari
This is a long overdue feature, and it’s kind of ridiculous it’s not the default. It’s also very Apple to call these “website icons” instead of “favicons,”.