Sidebar makes my Firefox pretty slow at startup and has a few bugs. I would love a native alternative with similar features. Namely I would really like vertical tabs that aren't a sidebar because I want to be able to use sidebars without hiding my tabs... But seems like this new implementation is also a sidebar.

Sidebery is fantastic, but I do feel like it's making things a bit slow. I might be prepared to give up on panels and nesting if I can get better performance. (And possibly the Tab Groups work can replace my use of panels.)

Maybe the native implementation is lighter, but yeah, I get it

My main issue with a non-native solution is that you need use userchrome hacks to make the horizontal tabs bar disappear, which doesn't sync between installations. I use Firefox in multiple computers at the school I work at, so it isn't a viable solution.