Indeed. It uses some of the vertical tabs features in Firefox, but adds workspaces (~tabbed tab window) that you can assign default containers (like banking, personal, shopping) to. Tab groups are missing, but are being worked on. Don’t expect nested tabs or trees like Sideberry or TST offer though. Honest disclosure: the implementation is not fully polished yet. The location where new tabs are opened or their remembered location after closing/opening the browser is not consistent.

Yes, I have tabs on the left and sidebar opens on the right.

Upvoted it. The inability to use a sidebar (local LLM chat) on the other side with vertical tabs or at all when using sideberry together with their changed stance on selling user data made me move to Zen browser.