Hi folks,
Thank you so much for all the feedback you've given us here, we really appreciate it. Our small group has been in a time crunch to polish the new experience, and I apologize for not being able to respond to individual comments. You brought up valid and interesting points, and I hope to address them slowly as the new sidebar evolves to a more polished state.
One note that I want to make though - we are currently not looking into creating a second sidebar. The screen resolution of most Firefox users is such that it is not something that would benefit majority of users, and in our studies people almost uniformly oppose it because of the lack of screen space. Second sidebar might work for people with ultra-wide screens, we might look at it in the future if we see that many people struggle with the interaction model we chose, but it's not a short-term priority.
We are currently working heads down on the very first version of the sidebar and vertical tabs, and the first, - still rough around the edges version - is now available as Nightly Firefox Labs experiment (you can find it by going to Settings > Firefox Labs). We have created a separate post to track the feedback for this first version.
