ℹ️ Edit
come on guys. 30 likes, 14 people gave a kudo? What kinda like is that? "Cool bro but not gonna make an account lol"
IF YOU WANT THIS, GIVE IT A REAL LIKE
If you want, vote for my proposal to allow 2 sidebars in Firefox!
Firefox gets vertical tabs and a sidebar, cool huh? And you can open pages as sidebar popups, for example a small dictionary page, or a notepad or whatever else!
But when using vertical tabs and these site popups, it looks pretty ugly and pushes the main site to the edge.
Having a sidebar and a vertical tab bar would fix this.
Current state and mockup as images attached.
This is how it currently is: the sidebar and the vertical tab bar are the same. Placed extensions are unintuitive and popup windows (like Mozillas SideView or dedicated extensions) are next to the tabs, pushing the main website even further to the side

This is how I would like it to be. A sidebar and a tab bar. Extensions go on the sidebar and the tab bar is just for tabs. The browser view is centered and clean.

(Tbh I would like tabs on the left but I am too lazy to edit the mockup)
What did you set to open the sidebar popup on the right? Btw pageassist is great
It's configurable from the sidebar dropdown menu, e.g. when opening your bookmarks (Ctrl+B):
But you can also use this
about:config
setting:Again you keep calling it a popup, but it really isn't. It does not pop up or overlay the browser viewport, it sits on the right and pushes the viewport left reducing its width.
It is kinda a popup. On Firefox if you change that config, the unified tab-sidebar moves around so this is useless.
Seems that Zen might do something different and not use the sidebar after all