Firefox 89 has hidden the "Compact" interface mode that makes the tab bar take up less vertical space than the "Normal" and "Touch" modes, and has marked it as

Firefox 89 has hidden the "Compact" interface mode that makes the tab bar take up less vertical space than the "Normal" and "Touch" modes, and has marked it as an "unsupported" feature. It may be removed in the future. If you want to provide feedback on this, Mozilla has opened a forum and this is already the most popular topic: https://mozilla.crowdicity.com/post/719764 https://mozilla.crowdicity.com/post/719764