Firefox

Tree style tabs, which gives vertical tabs that you can arrange in a hierarchy to keep related ones together

Simple tab groups, which lets you have multiple sets of open tabs you can switch between (can you tell I have a problem with too many tabs?)

Unstick!, which when clicked removes any sticky elements, i.e. parts of the page that stay on your screen while you scroll. It's great for removing all the bars and obstructions to reading that pages like to put in your way. For some reason I have to click it twice for it to work

Read aloud, a good text to speech extension to read pages or parts of pages to you. It can be used with cloud based neural voices from Google and Amazon with some setup

Consent-o-matic, which gets rid of the cookie consent popups for you and it's configurable as to which types of cookies it will refuse or consent to for you

SponsorBlock for YouTube, which can auto skip sponsor reads and various other kinds of segments you select to be skipped

A few short months ago I would have said RES but, well 🤷‍♀️