Well, to be more specific -- I want the OS itself to be a full-screen tab container with multiple spaces/desktops (and add tiling, and popping out tabs like floating windows, as advanced usage).
And then each tab is an app or app document window. So I could have a Chrome tab next to a Firefox tab if I wanted. Browser tabs would be peers next to other apps.
None of this is about security, or running apps in the browser. Just using tabs as the main concept for everything, rather than windows.
This bugs me too sometimes. It's incongruous that I can stack Gmail, docs, and my company's ticket system nearly into one tabulated window, but I have to use a completely different interface to access a local file browser, RDP, or the sniping tool.
It's funny, my version would probably just put every browser tab into a different window and just use a powerful window manager like i3 to deal with everything.
I am using i3 but what bugs me is that tabs now seem to be part of the browsers.
There's no elegant way of telling Firefox to never use tabs, always open a new window. There are some extensions pretending to this, but the experience is terrible. There actually is a new tab created which is then detached.
I don't usually use Chrome, so I looked up wether it handled this, but it seems to rely on extensions too.
Qutebrowser works, but it has other limitations, such as poor extension support.
I've had the exact same experience you described. Realizing i3 is the way to go and apps shouldn't manage tabs themselves - trying to stop Firefox / Chrome from doing so - realizing it's not simple and the no tabs extension is problematic. Trying qutebrowser and giving up because it's limited.
I've settled on NoTabs Firefox with a userChrome.css that hides the tab bar until Firefox someday supports native no tabs.
Sounds like Ubuntu's Unity to me. My 2 cents: Now that I'm using two 4K panels I very much enjoy having 4 windows side-by-side (optionally even splitting those vertical "columns" horizontally to hold 2 windows). No more task switching, all I need is always visible - I personally wouldn't opt for a tab-based full-screen WM.
I think this is doable today. Just disable tabs completely on Firefox and chrome, and use a window manager that allows you to group windows into tabs (like i3)
And then each tab is an app or app document window. So I could have a Chrome tab next to a Firefox tab if I wanted. Browser tabs would be peers next to other apps.
None of this is about security, or running apps in the browser. Just using tabs as the main concept for everything, rather than windows.