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.
For everything else there are network protocols, native apps and scripting.
Blocking ads, should be done at the network layer.
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
Houdini allows for low level control of CSS rendering, basically it allows for creating CSS classes with our own paint methods, and in the process having lower level JavaScript concurrency using less resources than workers.
