Firefox

I'll try and see what I can find bc the most of these things were done in a long periods of time and I'm not sure what is still findable. The "View image details" in particular you can see for yourself that it's missing. Simply open any image (except from Instagram - Firefox doesn't detect these correctly), right click it and you'll se there's no such an option. There's only "Inspect" from which you can get the URL but there's no more the additional window where you can see image dimensions, size or just click "save as...".

The disappearing interface bug that was never fixed: https://bugzilla.mozilla.org/show_bug.cgi?id=1536396

The anti-tracking function that causes some websites not to let you in - try logging into your mediafire account. It doesn't always happen but when it does, it will say "this form was idle for too long" and that's it. Eventually you'll have to change the browser in order to login.

The disabled function - you can see that one for yourself as well. Simply open the menu, click "Help" and then "Feedback". You will see this: https://i.imgur.com/NjvwTjm.png It's like that for about a year, probably longer.

The other removed features - such as status bar and disabling updates are clearly visible by anyone, so I'm skipping these.

As for the war against adblockers (mostly), here's an example of my about:config (I still have Firefox but it's not my default browser anymore): https://i.imgur.com/UEIaAcf.png This was my way to disable addons removal - setting url addresses as 127.0.0.1 bc Microzilla had blocked many addons (adblockers included) for unknown reasons and when that was implemented with a browser update, I turned out with a browser stripped off of half of its addons. Even an addon I've been using for years (previously known as Speed Dial, now known as GroupSpeedDial) was removed and marked as "dangerous" (a complete bullsh*t, ofc, there's nothing dangerous about it).