I recommend:

1. Ublock
2. Sponsor Block for Youtube
3. Return Youtube Dislike
4. Hide Shorts for Youtube (I actually like shorts, but only on my phone)
5. Stylus
6. Decentraleyes
7. Don’t Accept image/webp
8. Rotate Image (rotates images in 90 degree increments)

Since it hasn’t been mentioned yet, NoScript imo. Some sites run an absolutely absurd amount of scripts and the majority are not required for the site to function. So at best, there’s no value from letting them run.

Some that I use:

Dark Mode I don’t like having a light screen.

• Dark Reader. This does a pretty technically-impressive-to-me job of making reasonable dark versions of pages. It’s not perfect – there are a handful of sites that it needs to be toggled off for, makes something hard to read – but I’m amazed that it does the job it does.
• Blank Dark Tab: Replace the new tab with a blank page matching Firefox’s built-in dark mode

Privacy/Anti-Tracking/Ad-blocking

• uBlock Origin. Ad blocker.
• Privacy Badger. Targets cross-site tracking, EFF project.
• Decentraleyes. Targets CDN tracking.

Paywalls Some paywalls can be bypassed.

• Bypass Paywalls Clean

Tweaking Frameworks

• Stylus: Doesn’t do anything on its own, but permits collections of third-party themes to be applied to websites to fix annoyances.
• Greasemonkey. This doesn’t do anything on its own, but it permits people to publish little modifications to be applied to webpages, permits for a lot of little scripts that fix annoyances on websites. There were a number of useful scripts that I used on Reddit.

Misc

• Edit with Emacs. Permits opening the contents of a textarea in an external emacs instance. Nice for things like, say, writing a large lemmy post in Markdown. I vaguely recall that, at least some years back, there was a way to embed a version of vim in Firefox textareas, so if vim’s your cup of tea, that might be interesting, if it’s still around.
• Instance Assistant for Lemmy and Kbin. A variety of quality-of-life fixes for lemmy and kbin. Lets one open a given lemmy/kbin post on their local instance if they wind up viewing a page on a remote instance.
• Reddit Enhancement Suite. If you still use Reddit, this has an enormous collection of quality-of-life improvements for Reddit.

EDIT: I don’t know if this is the embedded vim that I recall, but Firenvim seems to do roughly the same thing, if not.

Dark Reader
uBlock Origin

Optional:
TWP Translate (is better than the new feature)

Flagfox if you wanna see where a site is hosted. Provides little actual benefit but it’s cool to have anyway!

All the ones that are most important to me have already been mentioned.

I really love the built-in container extension (Multi-Account Containers or something like that). Really good if you need to log in to the same site multiple times or if you don’t want someone track you across sites.

Might not be a useful plugin, but fans of Terry Pratchett might like the GNU Terry Pratchett idea. For librewolf I use this slightly updated add-on which fixes some minor issues (source available).

uBlock Origin and some kind of mouse gesture with rocker commands extension. Those are the only two universal types I use. Everything else I can’t live with is pretty specific to my own usage to alter the function of specific websites (like RES for Reddit, but for other sites).

For me, I cannot go without the flagfox extension on PC. Otherwise, I’d probably just be going over extensions everyone else has been beating like a dead horse.

Ublock origin

Nobody has mentioned DeArrow - an add-on that removes clickbait youtube titles and thumbnails. works like sponsorblock, by the same dev.

Deadname remover is also nice

uBlock Origin

KeePassXC-Browser (Or your preferred password manager)

Consent-O-Matic

LibRedirect

Bypass Paywalls Clean

• DownThemAll!

• Firefox Translations

• Imagus

• uBlock Origin

• Grammarly

Any extension to re-enable right click. It’s annoying when they try to block me from downloading a picture/video, copy pasting, or inspecting elements

Nobody mentioned Tridactyl yet so… Tridactyl. It’s the best vim keybindings extension for Firefox I’ve tried.