Option to put tabs vertically on the left/right side of the browser like in Edge.

[jscher2000]

There are a few add-ons that can list your tabs in the sidebar, but these can't hide the top tab bar, so they don't give quite the same effect. Still, it might be worth taking a look to see what you think:

• https://addons.mozilla.org/firefox/addon/tree-style-tab/
• https://addons.mozilla.org/firefox/addon/sidebery/