My tree style tabs have disappeared after Firefox update. It's not disabled.

Hello,

A theme is an add-on that changes the visual appearance of Firefox. You can switch to another theme as follows:

1. Click the menu button and choose Add-ons and themes.
2. Switch to the Themes panel.
   • The built-in default System, Light, Dark and Alpenglow themes will be listed, as well as any themes you installed yourself.
3. Find the theme you want to use and click the Enable button.

To uninstall any themes you installed yourself, click the ellipsis (3-dot) icon and click the Remove button.

For more information about Firefox themes, see the articles Use themes to change the look of Firefox and Built-in themes in Firefox - alternative to complete themes.

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Thank you, Phantom, but you've answered a different question.

My list of TreeStyle Tabs disappeared with the new version of FireFox. No amount of searching or clicking or hand-waving or cursing has brought it back, although it is listed as an enabled Extension in Settings.