I liked Zen but it was a nightmare to deal with on multiple devices and dealing with multiple windows broke a lot of the essential stuff like them being unpinned on one window but not the new one but the new one has the original window essential now also as a standard tab. And they kept changing the way you switch between workspaces without the necessary customisation options to change it back and any of the mods that “fixed” those issues would then break unless updating the files manually because their fixes had to be merged into the main repo that zen uses for mods which didn’t happen fast enough. So I gave up and and actually switched to edge briefly for it’s implementation of vertical tabs (which i still think is done the best) until Firefox proper gained a good enough vertical tab implementation and I’ve been there since.