Nook - Arc Style Folders & Pinned Tabs by james

Nook turns Firefox's sidebar into an Arc-style home for your tabs:

Pinned grid - your daily apps as favicon tiles at the top. A saved tab that's open is highlighted and deduplicated; clicking focuses the existing tab instead of opening another copy. Closing it keeps it saved.

Folders - file tabs into folders with emoji icons. Rename, collapse, "open all", drag things between folders, the grid, and Today.

Today - every open tab that isn't saved anywhere, in one tidy list. Drag to reorder your real tabs, shift-click to select a range and move tabs in bulk, and hit Clear to close everything except the active tab. Tabs open on your other synced Firefox browsers appear in the same list — click to open them here.

Sync - folders, pins, and themes follow your Firefox account to every Firefox where Nook is installed. No account, no server, no tracking: it all rides on Firefox Sync.

Looks - eight pastel gradients plus white, black, and an auto mode that tints the sidebar to match the site you're on. Follows your system light/dark mode. Collapse the whole sidebar to a slim icon rail with one click.

Safety net - a daily local backup of your folders and pins on each device, restorable from a right-click on the space name.

Pro tip - go full Arc: Firefox can't let extensions remove its own tab strip or the sidebar header, but a small userChrome.css file can hide both, leaving Nook as your only tab UI. A ready-made file with step-by-step instructions is here: https://github.com/jemesct/nook-firefox/blob/master/userchrome/userChrome.css

Keyboard: Alt+A toggles the sidebar.