edit: "isn't this implemented in-browser?" comments: maybe, but it's to the browser's implementation. These plugins are reviewable separate from their analogous browser implementation.
ToS;DR (Terms of Service; Didn't Read). It gives pages a rating based on their terms of service. It also provides you with a plain-english breakdown of the terms of a site/service.
No Script - Yes, I run both UBO and NoScript, they have slightly different use cases
Dark Reader
FireFox Multi-Account Containers
Redirector - Great for automagically changing links
KeePassXC-Browser - For password manager integration
Rested - For monkeying with REST APIs
User-Agent Switcher and Manager - Why yes, I am the browser you are looking for
Video DownloadHelper - Because sometimes, you need stuff available offline
In terms of actually recommending extensions to others. I'd recommend most of the above, excepting NoScript. If you are using UBO, then the use case for NoScript is a very narrow one where you want selective whitelisting of javascript while visiting a site. UBO's blacklisting approach works for most cases and UBO's whitelisting feature is lacking the granularity of NoScript.
Adnausem. Built on top of unlock origin it will simulate clicks on ads it hides to mess up your advertising profile. Also has an ad vault so you can see the adverts it is hiding.
Consent-o-matic. Run by a Danish uni, it will auto deny all cookie popups by actually opting out of everything for you.
Im using Firefox/a fork of it - please note that many of the below mentioned extensions either only exist for Firefox or don't work well with Chromium browsers due to manifest V3.
I usually don't get to post anything in these because everyone basically uses the same plugins to unfuck the internet
so heres a few that haven't been posted yet
LibRedirect - redirects common proprietary sites to a free and open source alternative
Tampermonkey - allows you to find and install custom open source scripts that add functionality to websites
I was a mad Opera user about 25 years ago, it was the best browser by miles at the time. One feature it had was mouse gestures. Mouse gestures and uBlock origin are the only two extensions I can't love without, but these lists never mention them so I feel like the only one who uses them.
It's hard to explain how cool and quick it is to be able to control your browser with the mouse. Open/close tabs, navigate tabs, back/forward etc. It doesn't sound useful, I'm usually a mad keyboard shortcut fiend. But with web browsing in particular, your hand is already on the mouse, scrolling.
The specific extension I use is Gesturefy, I encourage people to install it and give mouse gestures a go.
I'm surprised I haven't seen any recommendations for "Indie Wiki Redirect" as Fandom (the wiki site, common for games) has started shoving ads down users throats, so wiki maintainers are moving to other sites like wiki.gg, but search engines still show Fandom as the first result.
Not a full list, but these are my day to day extensions that I use the most:
UBlock Origin - (obviously)
600% Sound Volume - managing volume for tabs
Dark Reader - Dark theme, that works well for *most *sites. Sometimes I need to manually disable it for certain sites that don't play well, but that's pretty rare
Fake Data - fill forms with random generated data - for every site i need to sign up for and don't want to use PII
addy.io - extension for add.io email forwarding service (subscription needed) generate random emails for every website i sign up for that direct to my main email. If I start getting spam, I know which alias it came from and which site I made it for
password manager extension of choice - I prefer Bitwarden, but I get a 1Password subscription free with work so that's what I use to share password records with family
firefox container manager - very handy for work tabs, logging in with family credentials, etc
Imagus - displays bigger image when hovered over (Imagus Mod recommended);
Sponsor Block - Skips promotions on YT videos;
TOS;DR - summarizes TOS and Privacy Policies;
Cookie Autodelete - erases cookies when you close a tab, can make you log out regularly if you don't put an website on a whitelist, though.
Dark Reader - changes the page CSS and creates a dark mode version of any page, while it isn't always 100% perfect, it has many useful configurations, like whitelisting websites OR words on them, changing to a light mode, but less bright version of it, setting up the time that it activates, and a few more.
Open tabs next to current/Always Right - What the names says, 2 different extensions, but on Chrome I prefer to combine them.
Wayback Machine - has an option to auto archive, can bring you to oldest or newest versions of websites and links.
Search Image - gives you 6 or so options to search for an image online, kind of combines with Imagus.
uBlock Origin - the best ad blocker so far, browsers with built in adblock use it.
Privacy Badger - blocks hidden trackers once it sees then on 3 different websites
WhatFont - displays the font name in a popup, this is more a personal thing, but I enjoy it.
Anti fingerprinting extensions can possibly help.
This is a long list, but these are one of the extensions that I have and I most value, there are some otherb too, but those are more aesthetic than anything.
Despite uBlock, my first pick would be Tab Mix Plus. Firefox has yet to properly open up the API for tabs, so you still have to do some mucking around with internals, but TMP gives you multi-row tabs, specific tab-closing patterns, expanded right-click options, and a whole host of insanely useful tab features.
I have been using TMP almost since the beginning, a good 15+ years now, and consider it to be absolutely essential to a proper Firefox setup. I would be happy to punt my TMP config file to anyone interested.
Besides what everyone else already said: Vimium-C. It lets you use Vim bindings in your browser. It's also extremely customizable and even works with my bizzare keyboard setup.
Imagus feels like in an alternate universe it could be default browser behavior. When you hover over an image it will expand to full resolution and then you can press buttons to open in new tab, download, zoom in, etc.
Works on pretty much any website and is nice if the website has sized the images too small or if your eyesight is less than great.
These are a bit unique from the lists everyone else has, I think:
Lemmy Keyboard Navigation (like the kbd shortcuts from RES)
Google Popup Blocker (stop the annoying log in with Google popups everywhere on the web)
OneTab (this one lets you collapse a whole window of tabs down into a list in the OneTab tab that you can later reexpand into a window again when you re-attack whatever subject all the tabs were about)
These are the more standard ones that everyone seems to run:
uBO, Facebook container, Bitwarden, Privacy Badger. People say uBO already covers Privacy Badger but I like keeping it there because of the replace widget feature.
I haven't seen these mentioned but they are kinda niche though. I use them for work more than personal usecase but maybe someone else finds them useful.
Copy on select - highlighted text is automatically copied
Snap links - open multiple links or check several boxes using a click-drag interface
Outside of what has already been mentioned, I still don't care about cookies and cookie autodelete in tandem. The first accepts cookies. The second deletes them when you are done.
On my iPhone I have one called Save All Images. Basically you know how lots of sites especially any kind of social media where they want you there to see things… anyway they use a script or whatnot to prevent holding down on an image to get the save photo prompt. This is an extension that loads all images that are single level referenced and you can save any/all. I use it almost daily. Instagram, and the like, especially, they hate the notion of someone saving something.
In Firefox on my computer I have Element Blocker. Some websites just waste a lot of screen space so if you’re browsing a ton of content you’d like to get the most room, but some stuff takes up portions of the screen fixed and not movable. This extension lets you select an element and it makes it just disappear. It is absolutely essential.
Wayback Machine and also archive.is's addons. I archive webpages frequently so they're super helpful. And if a webpage has been taken down you can easily go to an archived version with the Wayback addon.
Also, Vimium C. Not for everyone and definitely down to personal preference rather than "I recommend this to everyone", but I'd struggle to browse the web comfortably without it.
Don't know if the other browsers have it, but I use Marker by robin-rpr on Firefox desktop. Simple Enough extension for being able to draw/annotate/highlight on browser screen. Was doing some college work in class and wanted to be able to quickly write out and convert binary. Helped so much to be able to do it in browser so I could easily see the numbers.
Though, it was last updated October 22, 2022, so keep that in mind if you're like me and don't always like using software that's more than a few years old (games not included). The alternative I saw (Web Marker by SFer) is under an "All Rights Reserved" license, but was updated last month (June 8th), so pick your poison.
Foxy Gestures. I love having mouse gestures for Close Tabs on Right, Back, and Close Tab, amongst other.
Zoom Page WE, automatically zoom to full width. Really useful for "convergence" pages, ie: lazy web developers that think every browser wants a 4 word wide column. You have to set "Automatically Zoom" in preferences, it doesn't work out of the box.