[adzii_nufc]

It's the play store asking for payment options. This is a default action as of the most recent store update. It's not mandatory however and can be skipped on that same page. As for YouTube, as per Mick's advice above, it's not browser related but can be reset as such by the app settings and clear data and clear cache for the YouTube app. Best to uninstall and reinstall via store and proceed there. There's no separate volume for YouTube via app, so if the other apps have sound then this should too.