Great module ! I just also wish a persistent volume setting by website (one for youtube, one for soundcloud, etc...), and also the possibility to boost the sound (for example a 0-200 volume slider instead of 1-100). Thanks.

Simply good. This extension does what it stands for: it globally overrides volume control across all pages with HTML5 video.
It's a good news when you're trying to amp up your tumblr dashboard but this causes all other pages to change volume too. So Youtube volume controls being completely useless while this addon is active.

I hope there is a way to implement whitelisting/blacklisting feature or even dashboard to manage volume settings per-domain and author will consider doing that.