How to reenable sidebar tabs after disabling them?

[SandyRodgers-2017]

I disable side bar tabs after install tree style tabs. I have since uninstalled tree style tabs. How do i reenable watefox's default side bar tabs. I can't find a button or option in settings. If it is in about:config I don't know what to change to get the button to come back. Could you help and maybe introduce an option that doesn't dissapear in settings.

[thunderstone135]

Look for browser.sidebar.disabled in $\color{deepskyblue}{about:config}$ and set it to false.