When using multi-window functionality with ripcord and smaller screens the tab-bar and topic/channel navigation takes up a ton of space. During normal usage this isn't an issue, but when 6+ windows are opened much vertical space is taken up.

Browsing through the tickets, making this a option is a bad idea (easy to disable and forget a combo). But showing it on hovering the global menu would be useable (as the global menu is always shown).

Thanks again for the great software!

Having a hotkey for this might be a worthwhile feature.
Many years ago I had my tabs relocated to my addons bar in firefox, this allowed me to toggle their presence with ctrl+/. Any other combination might work, but as long as it's an accessible combination it should be fine, as I assume some people would toggle these a lot.
There would be a entry in the View menu for it regardless

Which part of the UI exactly are we talking about collapsing? I can't exactly tell from reading the description.