Firefox

•uBlock Origin - I guess everyone knows this one •Privacy Badger - blocks trackers •Ghostery - blocks trackers, ads, scripts, etc.

You don't need all of that at once. Privacy Badger and Ghostery are redundant with uBlock Origin and Total Cookie Protection. Source: https://github.com/arkenfox/user.js/wiki/4.1-Extensions#-dont-bother.

Also, Ghostery is kinda shady in terms of opt-out tracking and showing ads to its own users. I don't know if they still do it, but my trust is already shattered and I see no reason to keep using Ghostery.

Not on mobile but on desktop Firefox Multi-Account Containers paired with Temporary Containers is a funcking godsend. Especially so when I'm doing web dev work.
Other that that uBlock is pretty high on the list as usuall.

Tab Snooze - allows you to close a tab and have it reappear at a chosen time later

Media URL Timestamper - automatically inserts the current timestamp of the YouTube/Twitch video you're watching and updates it in the history in case you accidentally close/navigate away from the page or go to a different time in the video

Feedbro - RSS reader with filtering capabilities

Redirector - auto-redirect specific URLs (for example, changing a YouTube Shorts url into a regular one, or changing Reddit links to always go to Old Reddit)

Undo Close Tab Button - allows you to restore recently closed tabs including the tab's history in the back button (max amount = browser.sessionstore.max_tabs_undo)

Violentmonkey - using userscripts that allow you to change things on websites.

• For Instagram - unmuting videos + setting their default volume
• For YouTube - disabling the subtitles/captions + disabling "autoplay next" for playlists + disabling autoplay of channels homepage video
  • a way to disable specific keyboard shortcuts (you need to manually add the code as a new script). I use /^(Key)?(End|I|O)|(Digit|Numpad)\d$/ instead of /^(?:Digit|Numpad)\d$/ (thanks to this post), to also disable the End/I/O keys in addition to the number keys.
• Note that, at least for Violentmonkey, if the userscript doesn't have the "://" part of the url in the @match line then you need to add it in the userscript settings after installing the script (for example, if the @match line of the script only has *.youtube.com/* then put *://*.youtube.com/* in the "@match rules" line in the settings)

YouTube Comment Reader - allows you to search through the comments of a video (by clicking on the addon in the Extension menu and then clicking on the "YouTube Comment Reader" at the top or the "X Comments" at the bottom of the tooltip)

Page Shadow - allows you to use dark and light themes on sites that don't have the option to change it.

And if you're like me and you find that some YT videos feel too slow but 1.25x is too fast, then you can use Enhancer for YouTube's "Playback speed" feature to have smaller speed steps. Then you can hold ctrl and use the scrollwheel (while over the video) to change the video's speed by the amount you chose (I use 0.05 speed variation, mostly changing to 1.05x or 1.10x)

• Vimium

• Redirector

(And OFC all the other great ones, Dark Reader, Chameleon, NoScript, AdBlocker Ultimate.)

I often use:

Not on mobile, but desktop:

• Enhancer for YouTube, I like it for having the “expand” making the screen bigger also cinema mode, toggling end cards off, boost volume — you can also take screenshots.

• uBlock Origin, of course

• SponsorBlock, which is a big extension that will auto skip sponsor readouts, selfpromos, and a lot of things YouTubers often do (sponsors, self promos, interaction reminders like liking and subscribing, intermissions, intros, previews, jokes, etc - you can choose to skip them or highlight them in the videos) it’s backed by community response, anyone with the extension can set up something to skip and share with everyone. Highly recommend if you’re tired of people pausing the video to talk about raycons or manscaped lol

Dark Reader: Especially late at night white page background just burns out my retinas, no idea how I ever managed before.

Ublock origin, Sponsor block, and NoScript

Haven't seen anyone mention Decentraleyes yet. Serves CDN assets locally to avoid CDNs as a vector for tracking or fingerprinting.

For me, it's many of the ones people have already said, plus:

• StreetPass (seriously cool - collects the mastodon profile of any website you visit where someone has set up the special link to their profile)
• Video Speed Controller (gives you fine-grained control over video speed, e.g. watching video at 2.6x speed)
• Privacy redirect (automatically redirects to various services, e.g. from Twitter to Nitter - can select a random instance each time)

ClearURLs

It makes, say, Amazon links not a three-page bookwork

Consent-o-matic !

Chameleon. My user agent changes every 30 seconds. Makes attempts to track me basically useless.