https://www.mrfdev.com/how-to-use-enhancer-for-youtube mentions a Toolbar for that extension, not a toolbar icon or "button". Right-click at the top of Firefox and see if there is a Toolbar added to the default Menu Bar and Bookmarks Toolbar.

Thanks for the reply. Covered that data, yesterday. There is NO ENHANCER TOOLBAR available when I right-click.

On my old laptop, when I installed Enhancer for YouTube, the icon immediately appeared on my Firefox toolbar. The icon was the link to the add-on's functionality and preferences.

"Manage" Add-ons is not an option...nothing to select to set preferences. I think it's time for UNINSTALL/RE-INSTALL.

01.24.20

UPDATE

UNINSTALL/RE-INSTALL worked just fine.

All is back to normal. Enhancer for YouTube re-installed automatically. All functionality and preferences normal

01.24.20