In Firefox 87+ the Library and the Home button aren't present by default on the Navigation Toolbar and you need to drag them out of the Customize palette to the toolbar. *https://support.mozilla.org/en-US/kb/customize-firefox-controls-buttons-and-toolbars Firefox 109 comes with the new Extensions button as the new way to manage your extensions. The Extensions button (puzzle piece icon) drop-down serves as overflow area for extensions you install, the classic chevron (>>) overflow area still exists but is only used for built-in toolbar buttons as found in the Customize palette. You can click the gear icon next to an extension or use the right-click context menu to pin the extension to the toolbar (Pin to Toolbar). To (re)move the extension from the toolbar back to the Extensions button drop-down, you can use "Unpin from Toolbar" in the right-click context menu. If you do not have extensions installed then this button takes you to about:addons (Tools -> Add-ons -> Extensions). *https://support.mozilla.org/en-US/kb/extensions-button The regular overflow area (>>) can only be used for built-in Firefox toolbar buttons as shown in the Customize palette and can no longer be used for extensions. For buttons provided by extensions, the Extensions button drop-down serves as overflow area ("Pin to Toolbar" and "Unpin from Toolbar"). ---- Later this year extensions will move their manifest from Manifest V2 to Manifest V3. With MV3 you have more control on what pages the extension is active (enabled) and you need to allow the MV3 extension for each origin. The new Extensions button provides the UI to manage those permissions and enable the extension for webpages and without this button you won't be able to place their button on the Navigation Toolbar and activate the extension. More info: *https://blog.mozilla.org/addons/2022/11/17/unified-extensions-button-and-how-to-handle-permissions-in-manifest-v3/

See also https://support.mozilla.org/en-US/kb/extensions-button