Since I keep a number of tabs open and can't find a post v57 extension that lets me keep multiple rows of all open tabs, its easy to get lost when tabs are scrolled horizontally off screen. This is a handy little reminder there are out-of-sight tabs.

Note, waterfox (branched from FF v56) supports all legacy functions and extensions, including an extension to use multiple tab rows & also to place tabs below the bookmarks (vastly clearer UI I can't understand why FF v57 dropped). Try Waterfox for support of all modern add-ons and all your favorite legacy ones. It shares the profile with FF and gives you back your old favorite add-ons and more.