X Dim Mode by juanbuis

X removed Dim — the dark blue background that used to sit between Lights Out and Default — and left you with pure black or pure white. X Dim Mode puts it back.

Dim returns as a fourth option inside X's own display settings, exactly where it always was. Pick it once and it stays.

Themes
• Dim — the original dark blue background, restored
• Five more to choose from: Slate, Jade, Plum, Dusk, and Ember
• Custom — dial in any color you want with the hue slider
• Applies everywhere: timeline, DMs, modals, the new chat UI, and X Pro

Extras — optional pieces of old Twitter
All off by default. Turn on only the ones you want.
• Classic bird logo — the bird instead of the X
• Classic font — Helvetica Neue, the typeface X used before Chirp
• Classic favicon — the Twitter bird back in your tab
• "Tweet, not Post" — the old wording, compose button included
• Start on Following — open on Following instead of For You
• Classic image grid — multi-image posts get the old grid, with nothing cropped off-screen

Easier on the eyes
Dark blue backgrounds cut halation: the glow that white text throws against pure black, which makes reading harder if you have astigmatism. That is why a lot of people used Dim in the first place, and why its removal was so unwelcome.

Privacy
No account. No tracking. No analytics. No data collection of any kind. The extension asks for exactly one permission — storage — which it uses to remember your settings. Those settings sync across your own devices through your Firefox account and go nowhere else.

Also worth knowing
• Works on x.com, twitter.com, and X Pro
• Runs on Firefox for Android as well as desktop
• Available in English, Spanish, Portuguese, French, German, Russian, Japanese, Korean, Chinese, and Arabic
• Open source: https://github.com/juanbuis/x-dim-mode

X changes its layout often, and when it does something here occasionally breaks. There is a "Report a problem" link in the popup — reports get read, and fixes usually ship within a few days.