What browser would be a seamless transition from Vivaldi?

Hi! I’m a HEAVY Vivaldi user for a long time now, it’s used on basically every machine I’ve used or owned. Though recently I’ve been encountering issues with it like slowdown, tab crashing, & the lack of widescreen support or at least “proper” widescreen support.

I’ve thought to myself about changing browsers. The problem being, I love every feature Vivaldi offers, side tabs, tab stacking, built in session manager, theming modularity and more.

Are there any non-Chromium based browsers that would be worth giving a good shot?