User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:93.0) Gecko/20100101 Firefox/93.0

Steps to reproduce:

1. Look at up left corner,
2. Vertical tabs button should appear here (like in MS Edge by default),
3. But vertical tabs button isn't here.

Actual results:

Vertical tabs button isn't anywhere, nor exists.
Add vertical tabs for better user experience with tabs.

Vertical tabs in edge: when you click button, then will appear a sidebar.

Expected results:

Vertical tabs should be in Firefox (like in edge).

Perhaps it would be good to have it as a built-in feature,
but there already exist plenty of addons for this functionality,
any problem using any of these? :
https://addons.mozilla.org/en-US/firefox/search/?q=tree%20tabs&sort=relevance&type=extension
https://addons.mozilla.org/en-US/firefox/search/?q=vertical%20tabs&sort=relevance&type=extension

The Bugbug bot thinks this bug should belong to the 'Firefox::Tabbed Browser' component, and is moving the bug to that component. Please revert this change in case you think the bot is wrong.

This feature was already requested in Bug 1698376, thank you for reaching out for this but I will have to mark it as a duplicate. Please follow the discussion there for updates on this request.