after using this, and accidentally found another add-ons called Sidebery. I think this needs to be developed further, because what is here is in the sidebery and even more features. Don't know why Firefox recommends these add-ons more than Sidebery

OK va bene

very heplpful

I love this addon so much. It's 90% of the reason I use FF over any other browser.

It's a must-to-have!
Would it be possible to add an optional vertical scroll bar? Or a way to speed up scrolling using the mouse wheel (w/ a key modifier), at least? It may take ages to scroll from bottom to top tabs when there's a lot of tabs.