Useful Firefox Extensions
By far my favorite part of Firefox is the extension library. I don't use all of these extensions, at least not actively; I enable and disable extensions pretty often depending on the context. Here is a combination of my extension recommendations and ones I've heard from other people.
Important note: Having a lot of extensions might fill up your extension toolbar, whch is to the right of your search bar and downloads button.
If you right click on an extension icon and click "remove from toolbar", you remove the extension icon. Or, you can click "pin to overflow menu", which will move the extension icon to a little dropdown in case you need to click on it sometimes. Use these buttons to keep your extension toolbar clean!
Account and Tab Management
Auto Tab Discard
While you're browsing, if you don't click on a tab for long enough (and it doesn't have an active form), the tab will go into a "sleep mode" where it still exists on your tab bar, but isn't consuming any memory, loading anything on the page, et cetera. When you click on the tab again, the page will load properly again.
This is great if you're one of those people who have 50 or so tabs at all times, 'cause it reduces memory usage.
Multi-Account Containers
Are you familiar with Chrome's "profiles" feature? This is exactly that, but not linked to a Google account! You can create a number of "containers". Each container is like a self-contained instance of cookies and all the websites you're logged into. You can even right-click an already-open tab, and move it into a container.
It's especially useful if you have a lot of accounts and need to switch between them without logging out and logging back in, or without going into private browsing.
Anti-Tracking / Anti-Capitalism
UBlock Origin
Oh baby we are doing this. UBlock is basically The adblocker. It blocks ads on damn near every website, even covering some bases that other adblockers don't. It also blocks trackers, pop-ups, miners, many other malicious URLs, and can even support your own custom filtering lists! Wanna block your follower count or the "trending" list on social media? I recommend it.
Some websites are really slimy and somehow use evil magic to evade UBlock. It's extremely rare and I only know one site off the top of my head that does it. That's right. Here's the adblocker for twitch.tv.
Privacy Possum
This extension sends false data to trackers to maintain your privacy and fuck up their data collection.
Important Note: If you use MSPFA.com, this will make it impossible to log in.
AdNauseam
This is like a combination of the above two extensions - more specifically, AdNauseam is a UBlock fork that not only blocks ads, but also sends garbage click data to them to make it look like you actually clicked on them. This wastes advertisers' time and money.
A big downside to AdNauseam, in my opinion, is that when I was using it, the ad-blocking lists were out of date or maybe faulty? So on certain slimy websites, the ads wouldn't be blocked at all. Combined with other privacy extensions, though, those unblocked ads shouldn't be tracking you anyway, they're just really annoying.
WhatCampaign
Did you know that a lot of sites add tracking parameters to the URLs themselves? Those "utm" parameters in a url - that's tracking parameters. This extension replaces all of them with FuckOff so the website can't use it.
It's completely unintrusive and ideally doesn't interfere with literally anything else, though rumor has it this makes some websites go into refresh loops (href.li links are susceptible.) If you remove the href.li part of the URL, it should work.
Better Browsing
Shinigami Eyes
Shinigami Eyes (yeah it's really called that) uses a database of people marked as either "trans-friendly" or "anti-trans" on social media and highlights their names for you. The extension supports different color schemes (bright red/dark green by default) and allows you to also personally mark links for your own notes.
I am not sure if the database is being updated anymore because the extension has been kind of inactive updates-wise since August 2021. Use your best judgement.
Some people who have rescinded their transphobia are still marked red, for instance, and the marking is by URL, not by account. So if someone changes their username on a website, and then someone else changes it to their old username, they may be marked.
XKit Rewritten
The classic Tumblr all-in-one improvement suite, now being rewritten from the ground-up. It doesn't have some of the original addons from the previous XKit, but it is being actively updated with new ones.
It has most of the essentials - No Recommended, Anti-Capitalism, PostBlock, QuickTags, Quick Reblog, AccessKit, Tweaks, and NotificationBlock, to name a few.
Redirector
This is a really simple extension that redirects from one URL to another based on your settings. I highly recommend this if you have a bad habit of engaging with sites and accounts that are actively detrimental to your mental health - we've all been there.
Inconvient Shit About Firefox / Chrome Features
Save Webp as PNG or JPEG
One of the annoying things about Firefox is that a lot of websites will encode their images as WEBP when loaded in the browser. This sucks because WEBP has artifacts like JPEG but less compatibility. My image editor program can't open WebP and yours probably can't either.
I don't use this one for saving WebPs as PNGs though, ironically - see the next extension. I use this because it's a faster "Save Image" button than the actual Save Image button.
Don't "Accept" image/webp
This extension auto-converts a lot of WebP-encoded images into PNGs instead, so if you find yourself unlucky enough to end up on a F*ndom wiki, this will be your savior.
Translate Web Pages
One of the few cool things about Google Chrome is that it auto-translates websites in another language using Google Translate. Of course it's not perfect, but it's pretty useful. Unfortunately, Firefox doesn't have this feature... but this extension is a pretty damn good "close enough".
You can set it to auto-translate pages, translate the page when you want it to, or highlight an individual piece of text, right click it, and then translate it.
Videos and Streaming Sites
TTV LOL
Ad blocker for twitch.tv.
BetterTTV
This adds various enhancements and features to twitch.tv. Do you notice that a lot of people in your streamers' chats use emote names that don't actually exist? A lot of them are BTTV emotes.
SponsorBlock
Youtube sponsorship blocker. This extension sections out intros, outros, sponsorships, interaction reminders, and promotions in a video's timestamp, and automatically skips over them. These timestamps are user-submitted and pretty much always accurate.
YouTube Screenshot
In my opinion this is one of those "you don't realize you need it until you have it" extensions. This adds a button in your YouTube controls bar that allows you to instantly screenshot a frame of a video.
A note about "Return YouTube Dislike"
I've seen YouTubers mention that this extension is completely useless, claiming the numbers aren't actually accurate. I cannot verify to you if they're lying though.
Honorable Mentions
This is stuff that I think is really niche and wouldn't recommend for the average user, but have been useful for me. Also known as the "low-effort summary" section because I'm not bothering with links and icons.
Tampermonkey
Popular userscript extension. Basically lets you download scripts (which are like mini-extensions) specific to a single website. It uses regular javascript for its userscripts.
Stylus
Similar to Tampermonkey, but for site CSS/themes. Do you hate the way a certain website looks, or wished a certain part looked different? This extension will help you.
Red Block
It's a Twitter chain-block extension (not to be confused with a blockchain). Go to any Twitter account and start blocking everyone who follows them. Blocks up to 500 people, and then you gotta wait out the rate limit so you don't get force-logged out of Twitter.
ChatReplay
If your favorite Twitch streamer has VODs uploaded to YouTube, but no chat visible, then this extension might show you the live chat replay of the VOD. Only streamer I've used this for is Jerma985.
Pinterest Save Button
Exactly what it says on the tin. Save any webpage to a Pinterest pin. Please don't use this on artists without their permission.
Allow Right Click
Some websites block your right click functionality. This returns it.
Twitter Media Downloader
Instantly download any video off of Twitter. You no longer have to ping that one bot in people's replies.
Wayback Machine
Instantly archive, or find web archives, of any website. Archive all of the sites and social media posts you love! You're gonna thank yourself if any of those things ever get deleted.