Since monitors are wide and websites are tall, we should very clearly put tabs on the side in a vertical stack. I was a heavy user of these in Firefox, and when I switched to Chrome I used their experimental --enable-vertical-tabs flag. When they removed it I wrote a post about how I love side tabs and switched back to Firefox:

I did end up switching back to Chrome as my primary browser (no post, sorry!), valuing speed and stability (relative to the Firefox of the time) more than side tabs.

When I started at Google in 2012 I asked the Chrome team if they could restore support for it, or at least make it be the kind of thing extensions could do. They told me that while they got this request a lot from Googlers, real users generally find it too confusing. And they were trying to build a "great defaults, no options" culture, to keep Chrome simple.

They've finally come around, however, and have added a "Show Tabs Vertically" option:

It does exactly what I want:

I suspect they came around on adding it because competing browsers supported it natively, and they were worried about losing users. I considered switching over this but it wasn't enough to get me to move: I trust Google's security team the most of these, and browser security is critical. Still, I'm glad others did, and now I have my favorite UI back after fifteen years!