Looking at the comments, interest in privacy and adblocking seem high. But the actual addons suggested here are often redundant or even worse, make you easier to track. Instead, take a look at the Arkenfox wiki, which is more or less the gold standard for browser privacy. Both LibreWolf and Mullvad Browser, practically the most privacy/anonymity oriented browsers out there, right behind Tor, either rely on it or stick very closely to it.
I highly recommend reading the entire wiki from the start. You dont have to do everything it says, obviously, but even if you dont do anything it will give you a better understanding of browser privacy. And lastly, do not use Chrome or any chromium based browser if you care about privacy and a free and open internet. Even if you only use a chromium based browser, you help increase googles monopoly.

uBlock Origin

Decentraleyes

Consent-o-matic

These are essential to me. Consent o matic automatically fills out cookie pop-ups by opting out of everything for you. Some of these cookie things take a while to process which shows how devious they are set up

• Adguard (Adblocker)
• ProWritingAid (Grammar Checker)
• Volume Master (Boosts tab audio)
• Chrome Remote Desktop (Obvious)
• Honey & Rakuten (Coupons and Cashback)

I also use a Chromebook, so I use these “native” extensions I developed.

• CrosKeys (Launcher, Clipboard Manager, Scripting, basically a Rofi replacement)
• CrosPaper (Wallpaper/Screensaver Manager)
• CrosManager (System Manager)

On Firefox:

• uBlock Origin
• Bitwarden
• Decentraleyes
• Terms of Service; Didn’t Read
• Firefox Multi-Account Containers
• Facebook Container
• Consent-O-Matic
• Don’t Track Me Google

…and the add-ons not related to privacy:

• 10ten Japanese Reader (Rikaichamp)
• Zhongwen
• New Xkit
• Earth View from Google Earth
• Palette Creator
• Save to Notion
• Send to Outline
• Web to EPUB

I use most of these on Brave Browser, too.

• AdNauseam (for cases when other extensions miss something)
• Bypass Paywalls
• Decentraleyes
• Don’t touch my tabs! (rel=noopener)
• Don’t track me Google
• Forget Me Not
• HTTPS Everywhere
• Old Reddit Redirect
• Redirector (to use the Vector theme on MediaWiki instances)
• uBlock Origin
• uMatrix
• User-Agent Switcher and Manager

More than I feel makes sense to post TBH. But a few important ones (for Firefox):

uBlock Origin
Sidebery to get my tabs in a vertical tree; if you often have more than 10-15 tabs I really recommend this!
Bitwarden (password manager)
Checker Plus for Gmail + Checker Plus for Google Calendar, easy-access email/calendar in a small window, I very rarely actually go to gmail.com
Return YouTube Dislike
Tampermonkey for userscripts on Kbin
Video Speed Controller, I use numpad +/- to increase/decrease speed by 0.25x, works basically everywhere including YouTube

Firefox:
UBlock Origin
DuckDuckGo Privacy Essentials Plugin
Decentraleyes

Brave:
UBlock Origin
DuckDuckGo Privacy Essentials Plugin

I dont use HTTPS Everywhere anymore because its included in Firefox and Brave!

Edit: I only use Brave to do my school homework because firefox messes with the website we use sometimes.

Augmented Steam
Bitwarden
ClearURLs
Cookie AutoDelete
Decentraleyes
Disconnect for Facebook
Don’t touch my tabs!
Enhancer for Youtube
Flagfox
Link Cleaner
NoScript
Privacy Badger
RES
Skip Redirect
Tree Style Tab
uBlock Origin
Undo Close Tab Button
View Image

Here’s my list. Using OperaGX.

• Bitwarden
• Buster
• Consent-O-Matic
• Dark Reader
• FastForward
• Picture-in-Picture
• Stylus
• TamperMonkey
• The Stream Detector
• uBlock Origin
• Session Buddy
• Return YouTube Dislike
• Looper for YouTube

Browser: Firefox, gonna name stuff i don’t see mentioned yet

‘Multi Account Containers’ + ‘Container Tabs Sidebar’ + ‘Switch Container’ + ‘Temporary Containers’ + ‘don’t care about cookies’ ‘Consent-o-matic’
basically allows you to easily have multiple accounts on websites while also making sure everything stays contained to its own bubble, and anything I don’t have a dedicated container for gets a temporary container that deletes the cookies after a bit in order for me to both not care about cookies and also not get any cookies. at this point mostly because I don’t like accidentally having an account on a non-contained instance

ff2mpv - easily launch videos in mpv, requires a bit of setup

Image Search Options - finding the source of most drawings, spotting which anime a clip is from etc

Yomichan for quick access to locally installed dictionaries (for Japanese in this case)
Toggle Clipboard

• UBO
• DDG Privacy Essentials
• LocalCDN
• Cookie AutoDelete
• TamperMonkey
• LibRedirect
• Keyboard Privacy

• AdGuard Extra

• AdNauseam (uBlock Origin fork)

• Bitwarden

• Clickbait Remover for Youtube

• Custom Scrollbars

• Don’t accept image/webp

• Enhancer for Youtube

• Proton VPN

• RES

• Return Youtube Dislike

• Sponsorblock

• Thumbnail Rating Bar for Youtube

• Tree Style Tab

• Translate Web Pages

• uBlacklist (no more deviantart trash in image search)

• Redditsave (probably won’t need this anymore since i moved here)

• vidIQ Vision for Youtube (information on screen pleases me)

• Violentmonkey

• Youtube-shorts block

and thanks to the based commenters here, learned there were some userscripts for kbin and got the Dark Reader extension

Here are the plugins I use:

• React Developer Tools (useful for developing with React)
• Ublock Origin
• Return Youtube Dislike
• SponsorBlock
• Grepper (shows convenient code snippets when I Google stuff)
• Cold Turkey Blocker (I use this to to block websites/apps when I need to focus)
• Shinigami Eyes (highlights queer friendly and anti queer subreddits/users/facebook pages/group differently)

On Firefox:

• uBlock Origin
• DuckDuckGo Privacy Essentials
• Privacy Badger
• SponsorBlock (skips the promotional parts of YouTube videos)
• Youtube shorts block
• 1Password
• Dark Reader
• Don’t Fuck With Paste
• Facebook Container
• Bypass Paywalls
• Disable HTML5 Autoplay
• Ghostery
• Old Reddit Redirect

I’m using Firefox:

1. uBlock
2. Darkreader
3. Privacy Badger
4. NoScript
5. uMatrix
6. Bookmark Dupes
7. CanvasBlocker
8. ClearURLs
9. YT Enhancer
10. FF Relay
11. Open in Private Mode
12. Open Tabs Next to Current
13. Secure Password Generator
14. Toggle web custom fonts