In Firefox 144, I can open vertical tabs and use Sidebery, but Firefox sidebar remains open on the side. I can remove it by setting always-show and hide-sidebar in config, but it reappears every time I restart.
Is there a way to permanently disable it?
Yes, tabs in Sidebery are “tree style”, you can build them into trees and collapse/expand them, also unload, group, bookmark whole branches and trees.
Vertical tabs are, well, just tabs stacked vertically. They are not nested, do not provide context, can’t be collapsed/expanded (or folded/unfolded, whatever you prefer). Sidebery just has many more features than just “woohoo you can see tabs vertically instead of horizontally” Firefox now provides.