ublock obviously should be installed on Firefox by default. But I seem to have a host of privacy add-ons that break few-to-no websites.

• Privacy Possum , which blocks certain tracking headers/js. Privacy Badger by the EFF is an acceptable alternative but I've personally found it doesn't block quite as much.
• NoScript Honestly my favourite addon of all time. You can operate in block-everything mode and just allow javascript/HTML5 from sites you trust, or if you're lazy then just operate in allow-everything mode and every now and then set crummy sites to untrusted (looking at you google tag manager). In block-everything-by-default mode, this add-on will break some sites, but the UI is so easy it's a couple of clicks to trust all the sites in a tab and auto-refresh.

Be warned - If you're not privacy conscious, you might cry from seeing the hundreds of sites that are running javascript on your machine without asking.

• User-Agent Switcher Really easy add-on to just leave on and misdirect sites. Never caused me a single problem, and in fact is useful when sites (looking at you Microsoft Teams) claim they don't work in Firefox and refuse to load but actually work fine if you use this addon and pretend to be Chrome.
• Sponsorblock kicks ass. 30 hours of ads skipped in half a year.

And my personal silly couple ones:

• Wikipedia Vector Skin because I'm an old fuddy duddy and I like old Wikipedia.
• Cat-In-Tab because I'm also an old fuddy-duddy that likes whimsy sometimes. This is just silly but I like it.