You can enable them in about:config if you search vertical.
Edit: to be more specific, the setting is 'sidebar.verticalTabs'
Great, thanks !
Also sidebar.revamp. It's kinda underwhelming, because as of now sidebar doesn't include tab titles and empty headerbar isn't removed. Hope it's going to be improved in the future
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You can enable them in about:config if you search vertical.
Edit: to be more specific, the setting is 'sidebar.verticalTabs'
Great, thanks !
Also sidebar.revamp. It's kinda underwhelming, because as of now sidebar doesn't include tab titles and empty headerbar isn't removed. Hope it's going to be improved in the future