Tab Groups. For those of us who do lots of research and like to keep it organized it's a godsend.

Right now I have 159 tabs open -- I was curious so I decided to count. If I tried that in Chrome I'm pretty sure it would crash and burn hard, not to mention there would be no ability to keep it organized.

I know there are some research workflows that would allow me to do that as well, but I haven't really taken the time to dive into them after I found tab groups.