Vivaldi, of course.
It's made by many of the people who used to make Opera.
It's now based on Chromium, so all those extensions work.
Give side tabs a try. It will be weird for a few days, and then you'll probably like it.
The more tabs you keep open, the better side tabs get.
Current Opera is also based on Chromium, and it has a few more tweaks than Chrome. I used that before Vivaldi.
I got tired of Firefox doing so many updates and breaking its own extensions, so I don't even bother with it as a secondary browser anymore. And Mozilla is too political to be taken seriously.