This extension was working great until recently. Not sure if it was an update to FF that broke it or what. My browser now shows the same tabs at the top as well. Im not sure how to get rid of those.

Everything works great! Though I can't make "Send tabs to other devices..." feature to work: sync is turned on, both devices are named and see each other in extension's settings. Guess I should log out and log in to set sync up again. Still great extension, the only one that does what I need

picture in firefox theme will be stretched as this addon's background, looks strange, hope for fix in furter updates.

Wow! Easy to use, and does just what it says. Press F1 to show or hide its list. If you wish, it's even possible to hide FF's normal (horizontal) tabs too, though it takes some fussing—see this PCWorld article:
https://www.pcworld.com/article/823939/vertical-tabs-in-firefox-yes-its-really-possible.html
Maybe this extension will eventually add that capability? (If so, they'd want to disable the F1 toggle, because you've got to have tabs somewhere, right?) Thanks for this great idea!