In no particular order…
When I encounter a new web browser, whether it’s from a fresh install or for whatever other reason, this is the first extension I go for. It’s a fantastic ad blocker that lets you use custom block lists that others have created.
Allows you to double-click on a word and see the definition in a little popup balloon. Real nifty. I find myself using it all the time.
Unfortunately, there isn’t a Firefox version of this extension. However, there is something similar: English Popup Dictionary.
My password manager of choice. I’ve tried others (LastPass and 1Password, primarily) and Bitwarden is by far the most consistent with syncing and mobile use. I’ve been using it for about 3 years without any issues.
Lets you see the technology that’s running the website that you’re on.
Similar addon for Firefox: Cookie Quick Manager.
Similar addon for Firefox (I have not tested this!) Lighthouse Report Generator
In conjunction with the ShareX Windows application, this is by far the best way to take screenshots and videos on your computer.
Forces HTTPS by default on all sites you visit.