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?
You might want to try CSS mods.
I don’t recall if they have exactly what you’re looking for (I prefer vanilla vertical tabs), but you can always make a request in their GitHub page. MrOtherGuy’s is one of the best Firefox CSS mods collections I’ve seen so far, and it’s regularly updated.
Edit: I think it’s this one? hide_tabs_toolbar_v2.css
Edit 1.5: Remember to have
toolkit.legacyUserProfileCustomizations.stylesheetsset totrueinabout:config. (The GitHub page has more instructions.)