BirdOne

One-line layout: tabs and unified toolbar share a single row, global search hidden (use CTRL+K).

Palette: Thunderbird's dark greys in FoxOne's tone, kept in Thunderbird's own lightness ratios, with an amber accent instead of the Windows accent colour.

Tested on Thunderbird 160 (Supernova UI, 115+ required) on Windows.

BirdOne is configurable through CSS variables. See all options → docs/customisation.md

Install both files: userChrome.css for the interface, userContent.css for the mail body, compose editor and settings page.

What about Firefox?

You are looking for FoxOne!

I want notifications only for selected accounts!

Oddly specific... but I got you covered: NotiFilter

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Installation and Customisation | Concept inspired by @NeroWolfe75's one-line experiment from 2023 | License: MIT