Much to my surprise, you can still download and use OmniWeb.

https://www.omnigroup.com/more

I only tried it on a few websites but it worked remarkably well.

The per-site settings feature was so easy to use; it also had "workspaces" so you could group tabs and open them all at once.

I paid for that browser and I still would.

OmniWeb was great! I think Opera still did it first, though.

I moved on to Safari after it died, but I missed vertical tabs dearly and still do. Hopefully this idea catches on well enough for the Safari team to finally steal it.

Opera was the Xerox PARC of web browsers in a lot of ways.

Except that you could actually use it instead of being a legendary project we only heard about but very few people actually used. That makes it all the more painful that it was taken away.

Yes, I remember Opera having it around that same time, and Firefox having a plugin to copy it. I think the Firefox plugin had full "tab tree" support though. I believe it died after one of the many updates that changed how plugins worked, although I haven't checked in a couple of decades to see if something similar has appeared.

You can still have tab tree in Firefox using Tree Style Tab (https://addons.mozilla.org/en-US/firefox/addon/tree-style-ta...)

Same here. I loved OW and its Tab layout. But after its demise I went to Safari.

Vertical tabs are already a thing in Safari with tabgroups although it doesn’t completely remove the horizontal tabs