Some Firefox addons I'm experimenting with (as of Firefox 62 or so)
One of the interesting things that's happened as a consequence of my switch to Firefox Quantum (ie 57+) is that I've become much more willing to experiment with addons. My pre-Quantum Firefox setup seemed prone to memory leaks due to addons, which made me fairly nervous about adding more; resigned to leaks or not, I didn't really enjoy the experience. My Firefox Quantum setup seems to be clearly better on all aspects of this (both initial memory usage and growth over time), and this has made me more willing to try addons.
Technically I'm getting most of my exposure to these addons through the latest Firefox master tree ('mozilla-central'), which I compile from source every week or so. But I don't think they do anything different in Firefox 61 or 62, and I have set up some of them there.
(Medium really is a plague and there is going to be a lot of carnage whenever it winds up shutting down, which I expect it to do within five or ten years at most. A lot of writing is going to disappear from the Internet and that bums me out.)
Certainly Something was pointed out to me on Twitter by @AleXgTorres. It's a quite thorough HTTPS connection information and certificate viewer. I don't use it very often but I care enough about TLS certificate stuff to keep it around in case (I have a history of having some such addon lying around), and it's not particularly obtrusive when I'm not using it. I could pick nits with the interface, but it's not that important in something that I only look at infrequently and CS's presentation of the certificate is traditional.
Finally I've recently added Link Cleaner (via the Mozilla blog entry) because I have to admit that I'm more than a bit tired of all of those utm_ fragments and other things. I sort of wish that it worked like my Google URL fixer addon and fixed the links in place, so that copying a link into some other program also gave me the de-utm'd version, but that's a minor thing. If I cared enough, well, LC's code is GPL3 and I could easily drop it into a version of my addon.
(The LC addon page is clear about how it works and there are probably benefits to cleaning the URL when it's actually used. Ultimately I don't care enough to go out of my way to deal with this; I barely care enough to use the addon when Mozilla basically shoved it under my nose.)
I've considered using 'Stylish' again (these days I'd use Stylus, since the actual 'Stylish' browser extension went bad), but I just don't seem to have much of a desire for re-styling websites these days. Most of what I want to do today is make annoying bits of websites go away entirely, and that's part of what I use uBlock Origin for. Possibly I could use some clever style override to deal with the header and footer plague, but my current answer is often to close the window instead.