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Were the icons moved to the toolbars? When did this happen?

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Specifically, which extension isn't appearing on a toolbar?

Recently there have been a few reports of a specific extension (or two) where the toolbar button was gone after an update or extension installation, and the button was found in Customize > Additional Tools and Features.

More than likely than happened due to the extension developer making major changes to their extension; and that should be a one-time-thing.