Add-ons not visible in toolbar customization
I have added many add-ons, some of them are visible in the screenshot. But i can't pin them to the toolbar. And therefore not able to use them. For some reason only three of them are visible when i click the plugin button in the toolbar and only one of them namely 'ublock origin' is pinned by default. I have tried many things but still not able to pin any plugin
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Firefox 109 comes with the Extensions button in the Navigation Toolbar as the new way to manage your extensions. The panel that opens if you click the Extensions button (puzzle piece icon) serves as overflow area for extensions you install. The legacy chevron (>>) overflow area still exists but is only used for built-in toolbar buttons as found in the Customize page.
In the Extensions button panel, 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 panel, you can use "Unpin from Toolbar" in the right-click context menu.
More Information:
Are you using Private Browsing mode?
I think cor-el figure it out with the last reply. If you compare the Extensions button drop-down with your Add-ons page, it's only the ones with the purple mask (extensions you allowed to run in private windows) that are on the list.