Pin Tabs
(Source: cultofmac.com)
Picked up by me just this year, I may be the last person to know about this feature. You can pin tabs in Safari and Chrome. I use it for my Gmail accounts and WhatsApp online. You right click on the tab for any page you wish to pin. A menu will pop up, granting you the option to pin the tab. Once you pin it, it slides over to the left where it stays until you close it.
