I just started using this extension a few minutes ago.
After many years of searching, it seems I finally found one that actually works like I want.
Sweet!

最高です！！
Android版Firefoxでも使えます。
PC・Android共に愛用しています。

Good

works as intended. im using it to boost sound on udemy videos works really well :)

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ประสบการณ์ทีมีประโยคช์ทีดี