Browser extension to return old Twitter layout from 2015 (and option to use 2018 design).
This extension doesn't add any CSS on top of original Twitter. It's fully original client that replaces Twitter, making it much faster than alternatives.

Chrome, Edge, Opera, Brave & Chromium browsers: Chrome Web Store
Firefox: Addons For Firefox

If you like this extension please consider donating:

• https://dimden.dev/donate
• https://patreon.com/dimdendev

• Almost all of Twitter functionality is implemented
• Both reverse chronological and algorithmical timelines support. And exclusive: Reverse chronological timeline with friends likes and follows (basically mix of both chrono and algo timelines)
• Custom profile link colors supported
• You can change custom profile link color and it'll appear for other extension users (priority: oldtwitter color db -> twitter color db -> default color)
• Removes all analytics and tracking from Twitter
• Track your unfollowers for free
• Search, sort and filter your followers
• Removes all ads
• Easy download of videos and GIFs
• Translate tweets without having to open them, also ability to set specific users/languages to autotranslate
• Shows why tweets were added to algorthimical timeline
• Dark mode support
• Ability to enable/disable Twemoji, disable stars (favorites) back to likes (hearts), change font, default link color and any other color in extension
• Lot of hotkeys
• Mobile support with Kiwi Browser or Firefox
• Custom CSS support

For beta version:

• You need Github account, please register if you haven't first!
• Go to Actions page
• Click on latest "Pack Extension" workflow run (first from top)
• Download OldTwitterChrome if you're on Chromium based browsers and OldTwitterFirefox if you're on Firefox

For stable version:

• Go to Releases page
• Download OldTwitterChrome.zip if you're on Chromium based browsers and OldTwitterFirefox.zip if you're on Firefox

• Unpack file anywhere
• Go to chrome://extensions
• Turn on Developer mode
• Press "Load unpacked" and select folder with extension
  

• Go to about:debugging#/runtime/this-firefox
• Press "Load Temporary Add-on" and select zip file you downloaded

Installing this way on Firefox will remove it after closing browser.

Yes, you can use Kiwi Browser to install it from Chrome Web Store or Firefox Beta/Nightly to install it from Addons For Firefox (follow these steps for Firefox). Once installed you can press on "Add to Home screen" button in Kiwi Browser to have it as standalone app.

The source code is available at GitHub so you can check everything yourself. It never sends any of your personal info anywhere.

Extension won't be pixel perfect copy of old Twitter. I just took general look and feel of it.

You had algorithmical timeline enabled. By default OldTwitter turns on reverse chronological timeline, you can switch it back to algorithmical timeline in settings or using the switch on the right side.

You need to add ?newtwitter=true to end of your current URL. There's also a "Open this page in new Twitter" button on all pages on bottom right.

Click on your profile picture on top-right and then Settings button.

There's a setting to use design from 2018.

You can disable all hotkeys in settings.

General hotkeys.
F - focus search bar.
ALT+F - unfocus search bar (only when search bar is focused).
N - open new tweet modal.
ALT+N - close new tweet modal.
ESC - close any modal.
M - open/close user menu (use TAB to navigate).
CTRL+ENTER - send tweet (when typing reply/quote/new tweet).

Navigation hotkeys.
CTRL+ALT+O - switch between old and new Twitter.
G+H - Home
G+N - Notifications
G+M - Mentions
G+P - Profile
G+L - Likes
G+I - Lists
G+M - Messages
G+S - Settings
G+B - Bookmarks

Active tweet hotkeys. On bottom-right of tweet element there's blue dot showing tweet is active.
S - move to next tweet.
W - move to previous tweet.
L - (un)favorite/like tweet.
B - (un)bookmark tweet.
T - (un)retweet tweet.
R - open reply box.
Q - open quote box.
C - copy tweet image.
D - download first tweet media.
SPACE - open full image / pause or resume video.
ENTER - open tweet in new tab.

These hotkeys work only when reply/quote box is opened.
ALT+R - close reply box.
ALT+Q - close quote box.

These will work when reply/quote/new tweet modal is focused.
ALT+M - upload media.
ALT+F - remove first uploaded media.

Help to translate this extension to your language.

English - dimden
Russian - dimden
Ukrainian - dimden
French - Aurore C., zdimension, Pikatchoum, adriend
Portuguese (Brazil) - kigidere, guko, prophamoon
Spanish - rogerpb98, gaelcoral, hue, Beelzenef, elderreka
Greek - VasilisTheChu
Romanian - Skyrina, AlexSem
Tagalog - Eurasian, @conc1erge, @cheesee_its
Latvian - yourfriend
Hebrew - "ugh", qqqq, kriterin
Nepali - DimeDead
Dutch - Puka1611
Japanese - Chazuru, Nyankodasu, kamokakesu
Korean - Nyankodasu, han_eirin
Turkish - KayrabCebll, YordemEren
Italian - krek, Francesco
Arabic - Yours Truly,
Thai - 0.21%BloodAlcohol
Polish - lele, nomi
Vietnamese - btmxh
Traditional Chinese - Oliver Tzeng（曾嘉禾）, cirx1e
Simplified Chinese - am1006, CarimoWuling
Czech - Menal
German - basti564
Catalan - elmees21
Swedish - actuallyaridan
Bulgarian - Scarlett7447)
Norwegian - twistquest
Indonesian - lorizade, Feerse_, DaGamerFiles