Second Bookmark Bar от softaware

Second Bookmark Bar adds a second, compact row of bookmarks right under Firefox's own Bookmarks Toolbar — it pushes the page down, it never covers your content.

Pin up to 7 folders to numbered slot buttons and switch between them with one click or a keyboard shortcut (Alt+1, Alt+2, Alt+3…), so your Work links, Design links, and personal links never have to share the same row. A Save button and a quick-save keyboard shortcut file the current page straight into whichever folder is active, and Save all tabs backs up an entire browsing session in one click.

Everything reads and writes ordinary browser bookmarks — nothing is imported, duplicated, or stored anywhere else. On top of the folders, Categories and Tags let you label individual bookmarks across folders, a built-in search finds a saved page in seconds, and a video-folder panel keeps a running list of videos with resume-from-where-you-left-off timestamps.

Free to use, with an optional Pro plan for people who want cross-device sync of their bar layout on top of Firefox's own bookmark sync.