(btw my browser is Firefox Nightly) Don't get me wrong, I love having vertical tabs. It's less busy than the horizontal tabs and I can look through my tabs more quickly. But, the way it's implemented sucks - It makes the layout of the webpage pop anytime I use it; there is no keyboard button attached to opening and closing the tab (I have to go through my horizontal bar to open my vertical bar); and recently my browser forgets the sidebar settings, meaning I have to re-check the "Hide tabs and sidebar" setting.

Bonus request Can the sidebar just go over the webpage (i.e. like the application menu) instead of squishing it? I'm ok with having some webpage features temporarily covered if it means I don't have to see the screen pop into a new rectangular shape every time I switch tabs.