Flagfox, not that useful but it’s interesting to see

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

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.

EDIT2: There’s also some “overlay remover” plugin that can bypass a number of obnoxious overlays that I use on my desktop, but I don’t have it installed on this machine. I think that it’s Behind the Overlay.

Other than ublock:

• Vimium to let you scroll and navigate with your keyboard.
• Your password manager of choice.

Basic Plugins:

• uBlock Origin
• Dark Reader
• Password Manager Bitwarden or KeePassXC-Browser. If you going to use KeePassXC. You need to download the manager itself.

Youtube

• Return YouTube Dislike
• SponsorBlock

Random Ones

• Indie Wiki Buddy
• Reverse Image Search
• FastForward

uBlock Origin.

LibRedirect for me, works well on both desktop and android

Foxy Gestures

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.

Ublock origin Ghostery Containers (so darn useful) Tampermonkey if you know JavaScript, little tweaks can make some sites much more usable

Custom Context search (forgot the actual name of it and I’m on mobile now). It allows you to add custom searches to your right click, so if you select text and right click, you can search for it on any site with search functionality.

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

Ublock origin

Surprised no one has mentioned VideoDownloadHelper yet - https://www.downloadhelper.net/

I’ve used this since I was a kid and it made me really popular in high school lol. Everyone thought I was a hacker or something.

uBlockOrigin, DarkReader & ProtonPass

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).