Because you're a "long tail case" tab user? Your case might be the poster boy for an active extension ecosystem that caters to niche needs.

I wouldn’t really expect base experience to match what it offers, so as long as Firefox doesn’t break extensions for power users, I am more than happy to see them experimenting with stuff that could help to win back some of the audience.

Because Mozilla is basically owned by Google, neither of them care about you or your UX, and Ladybird isn't ready yet.

Who says they don't? They've pushed 23 new releases since 2025 with thousands of updates that include exactly the bug fixes, performance improvements and security fixes you're talking baout. This latest release, v157, includes the built in dark mode you're asking about (I just saw it on the popup on first launch when installing this new version) and the release notes describe improvements to tabs. v156 included huge performance improvements and they're regularly pushing tons of CSS updates across practically all of the releases.

I don't understand why people claim these things aren't happening when they're regularly documented on their release notes page.

It has built-in dark mode, check out the Themes in your settings.

In fact, I propose that all computer User Interface design proceeds as:

    D(s) = (1 / (c * s + 1)) * (A(s) + N(s))

It means that both tabs get maximized and minimized at the same time, and the two tabs are always side by side. Which means if I need to jump to another task, like answering a message or joining a video call, I can get back to my work faster. It’s a small thing that helps with context switching.

I do it when I consider both side of the Split View one unified context I am working on. I do it not only with browser tabs, but sometimes terminal tabs. I most commonly do it with IDE tabs.

It makes a lot of sense if one uses subject-based browser windows (e.g. 1 window == 1 subject); it keeps all tab organization within the browser and makes it easy to minimize it, move it to different screens/desktops, save/restore it, etc consistently with less overhead (no secondary organization system [such as that of the window manager] involved).

This becomes even more valuable for cross-platform users who sync and can’t rely on their favorite uberleet-haxor-wm package being available everywhere.

Practically, it's most useful when I have two references for the same thing I want to move together as I work on that thing. E.g. Jira + Functional Spec as I do things related to them.

- The split view is a special looking tab you can come too easily. - You can have several split views in the same window. - Selecting what tab you want in the split view is much cleaner than tearing off tabs into windows. - No conceptual switch between "tab" and "window".