Firebug was probably the only add-on I ever cared.
For everything else there are network protocols, native apps and scripting.
Blocking ads, should be done at the network layer.
Blocking ads can be done both on app and net layers. I use both piHole and uMatrix (and uBlock Origin on the phone), piHole eliminates the worst offenders already and the addons can make more direct modifications to traffic.
i'm a developer and i find it hard to give a shit about any of that, container tabs are cute but they end up breaking a lot of websites, the rest is not even a blip on my radar
as for addons changing how my browser works - no thanks, i'd rather have a consistently nice browser experience than have to re-install addons everywhere
Firefox has developed Container Tabs, First Party Isolation, integrated Tracking Blocker, an early alpha for a password manager, Screenshots, Firefox Sync, DNS over HTTP and eSNI, not to mention that Mozilla lets addons do much more with the browser so an addon can really change how your browser works instead of being severely limited in what it can do.