are vertical tabs and the sidebar updates an a/b test?
i can't seem to find out how to enable them and everything i've read show options that don't exist in my install - i've also tried a fresh profile.
Wow! This is the first I heard of this so I looked it up.
According to this article it looks like you need a particular build thats not in the nightly mainline, and its very experimental.
Still, its exciting to see them work on this! I use Tree Style Tabs with custom userchrome.css, but it is a bit fragile. Native vertical tabs would be great!