According to Hands-on with Safari 9 in El Capitan: Little changes make a big difference (scroll down to Pinned Sites), there should be a Pin Tab option in the Window menu. That seems to be missing in my installation of Safari 9 in Yosemite. The article refers to El Capitán. Is this feature peculiar to EC? The other features seem to be there (although I can't speak for Safari Tab Mute because I not only don't see it but haven't had the opportunity to test it if it appears only when needed).

1. I do believe the Pin Tab, in Safari 9, is specific to El Capitan. ...It's under my Safari's Window menu. Additionally if one has Safari's Tab Bar showing, Control-Click (on the Tab Bar for the web page) will show a popup Pin Tab (or Unpin Tab) selection.

2. Audio Mute is also specific to El Capitan. ...The explanation about using this Muting is based upon seeing an Audio button in the Smart Search field and then, hovering one's cursor over the button will show the Mute option (then, simply clicking the Audio button either Mutes or Unmutes).

Fortunately for Jon and other Yosemite users this is not so: Audio Mute works just fine in Yosemite. Just try a site with videos (or audio) like MacWorld, and start one yourself or wait until one autoplays. See the speaker icon appear on the tab and respond with blissful silence when toggled off, without switching to the 'offending' tab if you went elsewhere.

I stand corrected, although when I was using Yosemite I was unaware the feature was available.

I made the Mute mention based upon seeing iMore's El Cap Safari detail, where the Mute Audio capability is mentioned just after mention of the Pinned Tabs. ...A leaping assumption on my part.

Audio mute works in Yosemite just as alternaut said. It appears, so far, that pbguy is right about pinning tabs only working in El Capitán.