There will be also sidebar tabs extensions in the no-xul-world. Tab Center Redux is already a WebExtensions (compatible with future releases). It still misses the part to hide the original tab strip but there will be an API in the future and in the meantime you can hide it via userChrome.css.
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There will be also sidebar tabs extensions in the no-xul-world. Tab Center Redux is already a WebExtensions (compatible with future releases). It still misses the part to hide the original tab strip but there will be an API in the future and in the meantime you can hide it via userChrome.css.